Yaroslav Zherebukh, after a huge win over Fabiano Caruana, the defending champion, is tied for the lead with Wesley So after Round 7.

The United States Championship has a surprising new co-leader: Yaroslav Zherebukh. Zherebukh joined Wesley So at the top of the leaderboard after a shocking win over Fabiano Caruana, the defending champion and the No. 3 ranked player in the world, in Round 7. 

So kept pace with a draw against Ray Robson. 

In other results, the struggling tournament veterans had an excellent day. Alexander Shabalov, a four-time champion, showed sparks of his youth to win a sparkling miniature against Jeffery Xiong, and Gata Kamsky, a five-time champion, won a nice game against Daniel Naroditsky.

So and Zherebukh have 4.5 points each, followed by Hikaru Nakamura and Varuzhan Akobian, who have 4 points apiece. 

In the Women’s Championship, there were no major shakeups as Nazi Paikidze, the defending champion, drew Anna Sharevich. Paikidze continues to lead, now with 5 points, followed by Sabina-Francesca Foisor and Maggie Feng, who each have 4.5 points. 

The two championships are being held at the Chess Club and Scholastic Center of Saint Louis. It is the ninth consecutive year that the club has hosted both events. The open tournament, a round-robin with 12 players, has a prize fund of $194,000. The women’s tournament, which is also a 12-player round-robin, has a prize fund of $100,000.

Zherebukh is a Ukrainian-born student at Saint Louis University. His win over Caruana was a calm, calculated execution. Caruana played a little too provocatively in the Breyer System of the Ruy Lopez. He must have surprised by how quickly his position fell apart:

Zherebukh, Yaroslav vs. Caruana, Fabiano
ch-USA 2017 | Saint Louis USA | Round 7.2 | 05 Apr 2017 | ECO: C95 | 1-0
Qe7 This is a typical position in the Breyer Variation. Positions like this are usually marked with long periods of maneuvering and careful strategic planning. It does not look like Black is playing ambitiously, but there is a lot of potential energy in his position, particularly in the hands of a strong player like Caruana.
26. f4! This is always a double edged decision for White. White's pieces have better access to the kingside, but, after exf4, the e5 square will be completely in Black's control. Black can position a knight or bishop there and I'm guessing that is why Caruana provoked f4. The problem is that Black's pieces aren't well positioned to take advantage of the change in the structure and his king on h7 is vulnerable on the b1-h7 diagonal. It will take several moves for Black to reorganize his pieces, which gives White enough time to begin an attack. The Black bishop on b7 is particularly poorly positioned.
26... exf4 27. Bxf4 Kg8
27... Nd7 28. Nxh5! gxh5 29. Bxd6! And White's advantage would be decisive.
29... Qxd6 30. e5+  )
28. Rf3! The threats to f7 pile up swiftly.
28... Bg7
28... Nd7 Black would have liked to play this move, but the problem would be:
29. Nf5! Or Nh5. This was clearly what Caruana overlooked -- White has more threats than just the pressure on f7.
29... gxf5 30. Rg3+ Kh7 31. Qd1! Nf6 32. e5! dxe5 33. Bxf5#  )
29. Raf1 Nd7 30. Bh6! Forcing the exchange of dark-squared bishops. The Black bishop was a very important defensive piece, so the exchange makes his position harder to defend.
30... Bxh6 31. Qxh6 Qf8 32. Qd2!? Zherebukh realizes that he does not have to be in a hurry.
32... Ne5
32... Qg7 33. Rxf7 Qxf7 34. Rxf7 Kxf7 35. Qf4+ Kg8 36. Qxd6  )
33. Rf6! Perfect control over the dark squares.
33... Rad8 34. Qg5 Qg7 35. Bd1 Bc8 36. Qh4 There were other things White could have done, but Black's position is just very difficult to defend.
36... Kf8 37. Qf4 Qg8 A sad move for Black to have to make, but Black he had nothing better to do.
38. Kh1 More preparation.
38... Re7 39. Bxh5 Finally the long awaited sacrifice! Black doesn't have a way to fight back. The rest was relatively easy.
39... bxa4 40. Bd1 Qg7 41. Bxa4 Qh7 42. Qg5 a5 43. Kg1 Qh8 44. R1f4 Qg7 45. Rh4 Nd3 46. Rh6 Ne5 47. Rf4 Bd7 48. Qh4 Kg8 49. Qxe7 Re8 50. Qg5 Bxa4 51. Rf6

It was incredible to see a player rated 2800 reduced to making moves like Qg8 and Qg7.

The fastest, and prettiest, game of the day was between Xiong and Shabalov. Shabalov’s extremely aggressive style hasn’t been serving him so well against the strong lineup in this championship, but kudos to him for not trying to change his style. In Round 7, that paid dividends as everything worked out for him:

Xiong, Jeffery vs. Shabalov, Alexander
ch-USA 2017 | Saint Louis USA | Round 7.6 | 05 Apr 2017 | ECO: B10 | 0-1
Ne4 Black has played the opening a bit oddly, but the idea behind his last move is pretty well known. Xiong replies in the most principled way: He tries to win the Black pawn on e4:
7. Nxe4 dxe4 8. Ng5 c5! A very nice and intuitive idea: Target the White center!
9. Bc4 O-O 10. c3 cxd4 11. cxd4 Nc6 12. Be3 The center is secure and e4 is about to fall, but Black still has:
12... Qa5+! 13. Kf1
13. Qd2 Or Bd2, which was perhaps the best decision. But then Black should already be able to force a draw and Xiong was feeling ambitious.  )
13... h6 14. Nxe4 Rd8 White has won the pawn, but his king is awkwardly placed and Black is threatening to equalize material by playing Nxd4. Xiong tries to preserve his material advantage.
15. f4 b5 16. Bb3 Nxd4! Xiong may have calculated this far and White does have some resources - but I think he underestimated how weak White's king position is. It is hard to calculate all the possibilities, so perhaps Xiong needed to sense that his king is not very safe and play accordingly.
17. Bxd4 Qb4 18. Qf3 Rxd4! 19. a3 Qa5 20. Nf6+ Bxf6 21. exf6 This position is hard to evaluate. White's king is weak, but he also has a lot of threats against the Black king.
21. Qxa8 Rxf4+! 22. Ke2 b4!! 23. Qxc8+ Kh7 24. exf6 Qe5+ And the White king will be checkmated.
25. Kd1 Qxb2 26. Rc1 Qd4+ 27. Ke2 Rf2+ 28. Ke1 Qd2#  )

The end of the game deserves a special diagram: Qb6 is a hard move to find, but both players probably calculated it quite a few moves earlier.

Xiong, Jeffery vs. Shabalov, Alexander
ch-USA 2017 | Saint Louis USA | Round 7.6 | 05 Apr 2017 | ECO: B10 | 0-1
21. exf6 Qb6!! This was a very hard move to foresee a few moves earlier when Xiong played f4.
22. f5 A desperate try, but it is too late.
22. Qxa8 Rxf4+ The Black queen and rook work beautifully together to mate the White king.
23. Ke2 Rf2+! 24. Kd3 Qd6+ 25. Kc3 Qd2#  )
22... Bb7 23. Qg3 g5 24. fxe7 Re8 25. Re1 Rf4+ 26. Ke2 Qd4

Against Robson, So played a very-well-thought-out pawn sacrifice in a typical Reti middle game. It may not have objectively been  the best move, but it was enough to get Robson confused:

Robson, Ray vs. So, Wesley
ch-USA 2017 | Saint Louis USA | Round 7.1 | 05 Apr 2017 | ECO: A07 | 1/2-1/2
1. Nf3 d5 2. g3 Nf6 3. Bg2 e6 4. O-O Be7 5. b3 O-O 6. Bb2 c5 7. c4 Nc6 8. e3 d4 9. exd4 cxd4 10. Re1 Re8 11. d3 Bc5 12. Ba3 Nd7 13. Nfd2 Nb4 14. Ne4 a5 15. f4 Be7 16. Bb2 Nc6 17. a3 b6!? It seems like a harmless developing move, but it is actually the start of a very complicated sequence. So is offering a pawn sacrifice. If White doesn't accept it, then Black have a comfortable game as he will have neutralized the White bishop on g2 with his own bishop on b7.
18. Nd6 Bxd6 19. Bxc6 Ra7 20. Bxd4 e5! 21. fxe5
21. Bf2! exf4 22. Rxe8+ Qxe8 23. Nc3 fxg3 24. hxg3  )
21... Nxe5 A really cool idea - and something So obviously calculated when he played 17...b6.
22. Bxe5
22. Bxe8 Bg4! Is the key move that was rather hard to foresee.
23. Qc1 Nf3+ 24. Kh1 Nxd4  )
22... Rxe5 White is still up a pawn, but his lack of development is beginning to create problems for him.
23. Rxe5 Bxe5 24. Ra2 There are many possibilities at this point, which actually makes Black's choice very hard. I think So does a pretty good job of navigating the maze. It is interesting to note how his moves appear to be natural and intuitive, as opposed to the computer's suggestions.
24... Re7 25. Kg2 Qd6 26. Bf3 Qe6! 27. Re2 Qh3+ 28. Kg1 h5 29. Qe1! Qf5 30. Nd2 Qxd3 31. Kh1 Qf5 32. Bd5 Qf6 33. Nf3 Bg4 34. Kg2 g6 35. Re3 Bd6 36. Rxe7 Bxf3+ A more natural reply would be:
36... Bxe7 And Black preserves both his bishops. So would probably have played this in different circumstances, but he was in time pressure and may have been worried about White playing Ne5, though it doesn't achieve much.
37. Ne5 Be6  )
37. Bxf3 Bxe7 38. a4 Black's king is still a bit safer and he may still have a chance for the initiative.
38... Kg7 39. Bd5! Even though the White king is more exposed, his bishop is as strong as Black's.
39... Bc5
39... h4 Would have kept more pressure on White, but a draw would still have been the most likely result.  )
40. h4! Qb2+ 41. Kh3 The White king is perfectly safe. Robson is essentially past the worst of it.
41... Bd4 42. Qf1 f6 43. Qe1 Be5 44. Qe3 Qb1 45. Kg2 Qc2+ 46. Kh3 Qf5+ 47. Kg2 Qg4 48. Qf2 Qd1 49. Qe3 Qb1 50. Bf3 Qc2+ 51. Kh3 Qf5+ 52. Kg2 Qc2+ 53. Kh3 Qf5+ 54. Kg2 Qc2+

Unfortunately for So, he let Robson off the hook in time pressure.

In Kamsky vs Naroditsky, Kamsky, a former challenger for the World Championship, showed he still had excellent intuition in positions arising from the Spanish opening. Black seemed to be doing just fine, and then his position suddenly collapsed:

Kamsky, Gata vs. Naroditsky, Daniel
ch-USA 2017 | Saint Louis USA | Round 7.5 | 05 Apr 2017 | ECO: C91 | 1-0
18. Qe2 There are many plans for both players in a position like this. Naroditsky plays a normal looking move to release of tension on the queenside, but he unexpectedly ends up under pressure.
18... Nb6 19. axb5 axb5 20. Bg5! Qd7 Black's idea is to deal with Bd3 (if, for example, 20...Rxa1) by playing Bc6. His idea makes sense, but he underestimated the danger from Nf5.
20... h6 21. Rxa8 Rxa8 22. Nf5! This is very annoying for Black, particularly because:
22... Bd8 23. Bxh6! gxh6 24. Qd2! Is a strong plan for White. Black isn't lost yet - far from it - but White hasa powerful initiative.
24... Bc8 25. Nxd6  )
20... Rxa1! 21. Rxa1 h6 Would have simplified the position, but White would still have an edge after:
22. Bxf6 Bxf6 23. Bd3! The weakness on b5 is surprisingly hard to defend.
23... Nc4 Though Black has b5 defended, for now, the knight on is awkwardly placed. White now has different ways to increase more pressure. The simplest is
24. b3 Nb6 25. Rc1 Forcing Black to play Ba6, which is an ugly move.  )
21. Rad1 Bd8 22. Nf5 Nc8 White has several good ways to continue, but I like Kamsky's choice. He doesn't go for the kill immediately, but instead improves his position strategically, taking advance of Black's poor dark-squared bishop and that his knight on c8 is stuck behind his own pieces. White's next few moves are quite classy.
23. Bxf6! Bxf6 24. Bb3 At the right moment, White can exchange Black's last active piece by playing Bd5.
24... Ra6 25. Qd3 Rd8 26. Nh2 Ne7 27. Ng4 Nxf5 28. exf5 Qc6 29. Ne3 Qc5 30. Bd5 Bc8 31. Be4 b4 32. Nd5 bxc3 33. b4 Fancy stuff.
33... Qa7 34. b5 Ra3 35. b6 Qa4 36. Rc1 Ba6 The pawn on c3 will fall soon. More importantly, the pawn on b6 will be impossible to handle. The rest was easy for White.
37. Qg3 Kf8 38. Rxc3 Ra1 39. Rxa1 Qxa1+ 40. Kh2 Qb2 41. Rc7 Qd4 42. Nxf6 gxf6 43. Qh4 Qxb6 44. Qh6+ Kg8 45. Rc3

The day was much quieter in the women’s section, but it might not have been if Sharevich had taken one of the many opportunities she had against Paikidze to plant her knight on c3:

Paikidze, Nazi vs. Sharevich, Anna
ch-USA w 2017 | Saint Louis USA | Round 7.1 | 05 Apr 2017 | ECO: A09 | 1/2-1/2
34. Ra5 The advantage had fluctuated throughout the game. Black had played simple, logical moves, while White had really struggled. But Sharevich now missed several chances to put more pressure on White.
34... Ndc7
34... Ndc3 Would have been more logical.
35. Bc6 Is the move that that Black was perhaps worried about, but after Qb8, Black's position would have been better. Black also had a pretty sequence that would have been almost immediately decisive, beginning with:
35... Qc7! 36. Bxb5 Bh3! White's pieces are just so badly placed that Black can play this way. The threat of e4 is crushing.  )
35. Na3 Nd6
35... Nc3 36. Bxc3 dxc3 37. Qxc3 Bxd3 Black could also play other moves, but this was the simplest, after which Black's pieces are much better positioned than White's.
...   )
36. Qc2 Kh7 37. Nc4 Ndb5 38. Nf1 Black still has a sizable edge. White's only hope would have been to put a piece e4, but even that would not have been enough.

As the old saying goes, the draw offer made by Paikidze was perhaps her best move in the game!

The only decisive results were in the matches between the teenagers. Maggie Feng played another nice game to win with Black against Emily Nguyen. And Apurva Virkud used some nice topsy-turvy tactics to beat Carissa Yip:

Virkud, Apurva vs. Yip, Carissa
ch-USA w 2017 | Saint Louis USA | Round 7.6 | 05 Apr 2017 | ECO: E81 | 1-0
Ned7 22. Ng4! A nice, intuitive pawn sacrifice!
22... Bxb2 23. Nh6+ Kf8 24. Nhf5 gxf5
24... Kg8! Would have been fine for Black, though the position is by no means fun for her to play.  )
25. Qxh7 Nf6 26. Qh6+ Ke7 27. Bb5 Rg8 28. Rae1 White play patiently, but she should have been in more of a rush.
28. e5!! Bxe5 29. f4 Rxg5 30. fxe5 dxe5 31. Qxg5  )
28... Kd8
28... Rxg5! 29. Qxg5 f4! And Black would have been safe.  )
29. exf5 Nxd5 30. Ne4 Qe7 31. Nxf6 Bxf6 32. Rxe7 Kxe7 33. Re1+ Be6 34. Bxf6+ Nxf6 35. fxe6

Before the championship began, it was a general consensus that only one of the big three — Nakamura, So or Caruana — could reasonably hope to win the event. But Zherebukh has forcefully inserted himself into the mix as a contender. Everyone still has tough matches ahead and it is increasingly clear that none of the players can be taken lightly. So would still seem to be in the best position, but a lot could happen in the last four games.

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Parimarjan Negi is an Indian grandmaster who is the second-youngest ever to earn the title (at 13 years 4 months and 22 days). Ranked No. 80 in the world, he is a junior at Stanford University. He can be found on Twitter at @parimarjan.