The blitz phase of the competition on Monday will decide the title.

For the fourth consecutive day, Hikaru Nakamura ended the Kortchnoi Zurich Chess Challenge tied for the lead. And for the fourth day in a row, he had a different co-leader.

After seven rounds at a time control of 45 minutes per player with 30 seconds increment per move, Nakamura, who is from the United States, and Ian Nepomniachtchi, who is Russian, have 10 points apiece, based on four wins, two draws, and one loss. In the rapid portion, wins have been worth two points and draws one. 

Viswanathan Anand, a former World Champion from India, trails by one point, while Vladimir Kramnik, a former World Champion from Russia, and Peter Svidler, a seven-time Russian champion, are another point back, with 8 points each.

Monday, the players will move to the blitz portion of the tournament, in which wins will be worth one point and draws a half point.  

Nakamura began Day 4 tied with Svidler for first place. Both players had 7 points, but Svidler could not gain ground in Round 6. Instead, he became Anand’s third straight victim, the result of a Sicilian sacrifice that paid dividends.

Viswanathan Anand vs. Peter Svidler
Korchnoi Zurich Chess Challenge | Zurich SUI | Round 6 | 16 Apr 2017 | ECO: B45 | 1-0
1. e4 c5 2. Nf3 e6 3. d4 cxd4 4. Nxd4 Nc6 5. Nc3 d6 6. Be3 Nf6 7. Qe2 a6 8. O-O-O Qc7 9. g4 b5 10. g5 Nd7 11. h4 Bb7 12. a3 Rc8 13. Bh3 b4 Svidler wants to open the queenside and attack Anand's king. Yet, the impending sacrifice - typical in Sicilians - keeps Black's king stuck in the center.
14. axb4 Nxb4 15. Nxe6! A lovely sacrifice. Anand gets two pawns for the sacrificed knight, and his bishop on e6 will protect the a2 square.
15... fxe6 16. Bxe6 Qa5 17. Kb1 Rxc3 Black would love to develop his kingside, but this simple move actually creates an additional weakness.
17... Be7 18. Bd4 Exploits the unprotected pawn. Black is running out of useful moves.  )
17... Rc7 With the idea of playing Nc5 and running the king to the queenside was reasonable.  )
18. bxc3 Nc6 19. Rh3 Be7 20. Bd4 Nc5 21. Bxc5
21. Bxg7!? Nxe6 22. Qh5+ Kd8 23. Bxh8 Nf4 24. Qg4 Nxh3 25. Qxh3 Qb6+ 26. Kc1 Qxf2 Is messy. Anand evidently preferred to keep more pieces on the board, particularly his bishop on e6.  )
21... Qxc5 22. f4 White has a rook and two pawns for a knight and bishop. The pieces tend to outclass the rook when they are active. In this position, Black's pieces are restricted by the mass of central pawns.
22... Kd8 23. Qe3 Qxe3
23... Qb5+ Would have been my choice. The endgame is unfavorable, so deferring the queen trade seems optimal.  )
24. Rxe3 h6 25. c4 hxg5
25... Bc8 Is sensible. The bishop on e6 is White's best piece, whereas Black's bishop on b7 was not doing too much.  )
26. hxg5 Rf8 Svidler must have underestimated Anand's reply.
27. f5! Not only is the pawn immune, but the threat of f6 followed by g6 is lethal.
27... Ne5
27... Bxg5 28. Rb3 Kc7 29. c5! Is problematic. White wins material, and is infiltrating.  )
28. Rg1 d5 Desperation. As long as Anand does not blunder the skewer ...Bc5, he is winning.
29. Rb3 Kc7 30. cxd5 Rh8 31. f6 Bf8 32. d6+ Svidler resigned, as when the dust settles he will be down a full rook.

Meanwhile, Nakamura downed Boris Gelfand of Israel by outplaying him in an equal ending. Gefland got his bishop trapped in the corner. To save his piece, Gelfand had no choice but to hand his opponent an outside passed pawn. Nakamura converted his advantage with ease.

Boris Gelfand vs. Hikaru Nakamura
Korchnoi Zurich Chess Challenge | Zurich SUI | Round 6 | 16 Apr 2017 | ECO: D37 | 0-1
1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Be7 5. Bf4 O-O 6. e3 c5 7. dxc5 Bxc5 8. a3 Nc6 9. Be2 dxc4 10. Bxc4 Qxd1+ 11. Rxd1 a6 12. Bd6 Bxd6 13. Rxd6 Rd8 14. Rxd8+ Nxd8 15. Bd3 Bd7 16. Ke2 Kf8 17. Rd1 Ke7 18. Ne5 Nc6 19. Nxd7 Nxd7 20. Ne4 Rc8 21. Rc1 Nd4+ 22. Kd1 Rxc1+ 23. Kxc1 Nc6 24. Kc2 Chances are equal. But with his next few moves, Nakamura shows he is looking for a fight!
24... f5 25. Nd2 g5 26. b4 a5 Nakamura's pawn pushes have gained him nothing more than space. The position remains totally level, but Gelfand must have understood his fearless opponent's intentions.
27. bxa5 Nxa5 28. Be2 Nf6 29. Kc3 Nd5+ 30. Kc2 Nf6 31. Kc3 Kd7
31... Nd5+ Would have led to a repetition that Nakamura clearly did not want.  )
32. h3 Kd6 33. Nc4+ Nxc4 34. Kxc4 Still equal, but Nakamura's more advanced pawns give only him unlikely winning chances.
34... b6 35. Kb5 Kc7 36. Kc4 h5 37. Bf3 h4 38. Ba8 I'm not a fan of how Gelfand has played this ending, but he is still absolutely fine. However, his bishop is out of place on a8.
38... Nd7 39. f4 Gelfand can't retreat yet because:
39. Bf3?? Ne5+ 40. Kd4 Nxf3+ 41. gxf3 g4 Breaks through: the h-pawn will promote.  )
39... g4 40. Kd4?
40. Kb5 Would have held the balance. Clearly, Gelfand overlooked Nakamura's 40th move. Admittedly, Kb5 is an odd move to play - it feels like Black is about to maneuver his knight to the kingside. However, as soon as the knight moves to f6, Gelfand would retreat his king back to c4. It would be a draw.  )
40... b5! Amazingly, Nb6 threatens to trap the bishop!
41. hxg4
41. e4 Nb6 42. exf5 Nxa8 43. fxe6 gxh3 44. gxh3 Kd6 45. f5 Nb6 Is winning for Black. White has no way to keep both a3 and h3 defended, so the knight will jump around the board and win the game.  )
41... fxg4 White is out of useful moves.
42. Be4 Nf6 43. Bd3
43. Ba8 Nd5 Cuts off the bishop, allowing Nakamura to promote.  )
43... g3 44. Bf1 Ng4 Gelfand resigned. The threat of Nh2 is impossible to stop. The king and pawn ending, once White retreats with Kd3-e2, is lost.

While Kramnik could not make headway against Grigoriy Oparin, a young Russian compatriot, Nepomniachtchi scored a seamless victory over Yannick Pelletier of the host country of Switzerland.

Ian Nepomniachtchi vs. Yannick Pelletier
Korchnoi Zurich Chess Challenge | Zurich SUI | Round 6 | 16 Apr 2017 | ECO: A30 | 1-0
1. c4 Nf6 2. Nc3 c5 3. g3 e6 4. Nf3 b6 5. Bg2 Bb7 6. O-O Be7 7. Re1 d6 8. d4 cxd4 9. Nxd4 Bxg2 10. Kxg2 O-O 11. e4 a6 12. b3 Qc7 13. Bb2 Nbd7 14. f4 Rfe8 15. Qf3 Bf8 16. Rad1 Rac8 17. Re2 Qb8 18. g4 e5 19. Nf5 g6 20. Ng3 exf4 21. Qxf4 Re6 22. g5 Ne8 23. Nd5 Ne5 24. Rf2 Rc7 25. Nxc7 Qxc7 26. Ne2 Bg7 27. Nc3 Qb7 28. Nd5 Nc7 29. Ba3 Qb8 30. Ne3 Ne8 31. Ng4 Re7 32. Nh6+ Bxh6 33. gxh6 Re6 34. Bb2 f6 35. Rd5 Nf7 36. Qg4 Nc7 37. Rd3 Qe8 38. Rxf6 Nxh6 39. Rxe6 Nxe6 40. Qh4 Nf7 41. Qf6 Qd7 42. Kg1 Kf8 43. e5

Nakamura ended Anand’s winning streak in Round 7 and secured at worst a tie for the lead by making a draw. Svidler and Kramnik also drew, in 30 moves, after little excitement. 

The remaining two games were paragons of how to win with the Black pieces. Pelletier made a poor decision to repeat the opening from an earlier blitz encounter against Gelfand. In the post mortem the top Swiss player stated that he had not let his engine evaluate the position for long enough, instead relying on the instant feedback that White was better. Thus, Gelfand was able to halt his three-game losing streak by hunting down Pelletier’s king.

Pelletier, Yannick vs. Gelfand, Boris
ZCC 2017 - New Classical | Zurich | Round 7.2 | 16 Apr 2017 | ECO: D45 | 0-1
1. Nf3 d5 2. d4 Nf6 3. c4 c6 4. Nc3 e6 5. e3 Nbd7 6. Qc2 Bd6 7. b3 O-O 8. Be2 b6 9. O-O Bb7 10. Bb2 Qe7 11. Rad1 Rad8 12. Rfe1 Rfe8 13. Bf1 e5 14. cxd5 e4 15. Nh4 Pelletier deviates from his choice in an earlier game against Gelfand. In that game, Gelfand sacrificed his pieces to deliver checkmate (even if it should not have worked out).
15. Ne5 Nxe5 16. dxe5 Bxe5 17. dxc6 Bxh2+?! 18. Kxh2 Ng4+ 19. Kg3 Qe5+ 20. f4 Qh5 21. Rxd8 Qh2+ 22. Kxg4 h5+ 23. Kg5 Qg3+ 24. Kxh5 g6+ 25. Kh6 Qh4# Was how the blitz match between these two ended.  )
15... Bxh2+ 16. Kxh2 Ng4+ 17. Kh3 Ndf6 The bishop is coming to c8, leading to a number of great discovered checks.
18. g3 g5 19. f3
19. Ng2 Qd7 Is devastating. The king can't escape discovered (double) check.  )
19... gxh4 20. Nxe4
20. fxg4 Had to be played. Even if that also loses, it presents a much more difficult task than the game continuation, which didn't net White any extra material for his troubles. Pelletier should have been greedy.
20... Nxg4 The attack rages on. The knight is immune:
21. Kxg4 Bc8+ 22. Kh5 h6 Leads to mate.  )
20... Nxe4 21. fxg4 Qd6 22. Qg2 hxg3 23. Qg1 g2! An awesome way to conclude the game. Gelfand frees g3 for his queen or forces Pelletier to entomb his own king.

Oparin was solid in Round 6 against Kramnik, but against Nepomniachtchi he became uncharacteristically aggressive. His intentions backfired as he lost first a pawn and then a piece. His desperate attack sputtered, allowing Nepomniachtchi to catch Nakamura.

Oparin, Grigoriy vs. Nepomniachtchi, Ian
ZCC 2017 - New Classical | Zurich | Round 7.3 | 16 Apr 2017 | ECO: B90 | 0-1
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Qd3 Nbd7 7. Be2 g6 8. Bg5 Bg7 9. O-O-O h6 10. Bh4 O-O 11. Kb1 Qc7 12. Qe3 I'm not a huge fan of this move, as it is the second queen move made in the opening stages of the game. Now Nepomniachtchi can continue naturally, developing an initiative on the queenside.
12... b5 13. g4? Oparin does not have very realistic attacking chances, so this move just weakens his kingside.
13... Bb7 14. g5
14. f3 Does not actually save the pawn. Black simply launches his pawns:
14... b4 15. Na4 e5 16. Nb3 Bc6 The knight is trapped!  )
14... hxg5 15. Bxg5 b4 16. Nd5
16. Bh6! Was overlooked by both players. Granted, Black can simply play
16... Bh8 Because the extra sacrifice leaves Nepo with a strong, unchallenged dark-squared bishop.
...   )
16... Bxd5
16... Nxd5 17. exd5 Nb6 Would pick off the pawn on d5 as well, but Nepomniachtchi understandably wanted to use his knights to protect the kingside.  )
17. exd5 Nxd5 18. Qe4 N7f6 19. Bxf6 Black likely was happy to see this move: the dark-squared bishop could have been used in both attack and defense (retreating to c1) and the knights can get in each other's way.
19... Nxf6 20. Qg2 Rfc8 21. h4 Oparin loses a piece. His 'attack' does not exist.
21. f4 Barely helps. The pawn on c2 is now defended, but Black has an extra pawn and an attack brewing, so White is losing.
21... e5 22. fxe5 dxe5 23. Bf3 Rab8 24. Nb3 a5  )
21... e5 22. h5 exd4 23. Bd3 Nxh5 24. Rxh5 gxh5 25. Rg1 f5 26. Bc4+ d5! A precise move that opens the c-file. Otherwise White gets counterplay.
26... Kf8 27. Qg6 And Black would need to be careful not just to win, but to avoid defeat.  )
27. Qxd5+ Kh8 28. Bb3
28. Rh1 Is too slow.
28... Qxc4 29. Rxh5+ Bh6 30. Rxh6+ Kg7 And White has run out of useful checks.  )
28... d3 With 29...Qe5 looming, Oparin resigned.

Five players still have a chance to win the tournament on Monday, though Nakamura and Nepomniachtchi, who are both blitz experts, would seem to have the best chance.

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Robert Hess is a former United States Junior Champion, recipient of the 2010 Samford Award (the most prestigious in the United States for young players) and was runner-up in the 2009 United States Championships. A 2015 graduate of Yale University, he is the chief operating officer of The Sports Quotient, a statistically-based sports site that he co-founded. He can be found on Twitter at @GM_Hess.