The leader after four rounds finally lost, while So won his third consecutive game.

Tata Steel has a new leader: Wesley So of the United States. So, who had been tied for second after four rounds, won his third consecutive game to seize the lead after Pavel Eljanov of Ukraine, the leader since Round 1, finally lost.

So now has 4 points, followed by Eljanov and Magnus Carlsen, the World Champion from Norway, who each have 3.5 points. 

So is continuing his incredible stretch of play during the last few months, in which he has won the Sinquefield Cup, the London Classic and the Grand Chess Tour, a year-long series of super tournaments. During this stretch, So has run up an unbeaten streak of 49 games.

Eljanov had White against Levon Aronian of Armenia and I expected him to play a low-risk opening. Indeed he did, as he chose the Catalan. But low risk is not the same as no risk, and it’s not possible to choose a line in which errors will not lead to a bad position. Eljanov had an off day, and Aronian won a fine game.

Eljanov, Pavel vs. Aronian, Levon
Tata Steel Masters | Wijk aan Zee, the Netherlands | Round 5 | 19 Jan 2017 | 0-1
Rad8 This position looks level, but the difference in the minor pieces knight vs. bishop can create some imbalance.
25. Rc4?! A step in the wrong direction. Now Black's knights find good squares.
25. Bf1! This would have disturbed Black's coordination because
25... Nc6 Is a bad move because of:
...  26. Bxb5 axb5 27. a6  )
25... Nc6! 26. Qf4 Rd7! Black wants to double his rooks on the d-file.
27. Ne1 Nbd4
27... Rd4! This move was even better.  )
28. Qe3 Rfd8 Black's rooks are much better positioned than their White counterparts, and the Black knight on d4 is very effective.
29. h5?
29. Nc2 This move was necessary to limit the problems in White's position.  )
29... Nf5! The White queen doesn't have any good squares.
30. Qc5
30. Qf4 Rd4  )
30. Qc3 Ncd4  )
30. Qb6 Nxe5  )
30... Qg5! 31. Bxc6 bxc6 32. Qxc6 Qxh5 This pawn exchange leaves White's king very exposed.
33. Qf3 Qg5 34. b4 Rd2
34... Rd4 This might be even stronger, but the move played by Black is very natural.  )
35. Qf4 Qxf4 36. Rxf4 Rb2 Even in the endgame, White's problems persist. The White queenside majority is not mobile, Black can advance his pawns on the kingside, and Blacks rooks are active and well positioned.
37. Rc1? A blunder, but Bhite was already in significant trouble.
37... Nd4 White resigned as he must lose an exchange.

Eljanov’s loss opened the door for So and he came through against Pentala Harikrishna of India, who erred in the opening and was never able to recover. 

So, Wesley vs. Harikrishna, Pentala
Tata Steel Masters | Wijk aan Zee, the Netherlands | Round 5 | 19 Jan 2017 | 1-0
5. Nc3 d5? This is not a good move in this position.
5... O-O This move is better. Black would seem to be okay after
6. d4 cxd4 7. Nxd4 Qc7 8. b3 d5!  )
6. d4! cxd4
6... O-O 7. dxc5 dxc4 8. Qxd8 Rxd8 9. Ne5 This position is also no fun for Black.
9... Nbd7 10. Nxd7 Nxd7 11. Bg5  )
7. Nxd4 dxc4
7... e5 8. Qa4+!? Bd7 9. Ndb5 d4? 10. Bxb7  )
8. Qa4+ Nbd7 9. O-O! O-O 10. Rd1! White is being very patient. The pawn on c4 is not going anywhere, so first White works on restricting Black's development.
10. Qxc4 Nb6 And Black would be more or less okay as he can develop his pieces.  )
10... Nb6 This holds onto the extra pawn, but after
11. Qa3 What can Black do about the upcoming discovered attack on his queen?
11... Qd6 An unfortunate necessity for Black.
11... Bd7 12. Bxb7  )
11... Qe8 12. Ndb5 Threatening Nc7.  )
11... Qc7 12. Ndb5 Qb8 13. Qxe7  )
12. Qxd6! exd6 13. a4! So far, this game had followed one played between Vladimir Kramnik and Ian Nepomniachtchi, which Black lost badly.
13. Bf4 d5 It's not that easy to dislodge the knight on b6  )
13... a6
13... a5 14. Ndb5 d5 15. Be3 And White has a decisive edge.
15... Ra6 16. Nc7  )
14. Bf4 d5 15. a5 Nbd7 16. Rac1 Patient, simple and strong. White will eventually win the pawn on d5.
16. Nxd5 Nxd5 17. Bxd5 Nc5 Black is much worse, but he can fight on for a while.  )
16... Rd8 17. Bc7 Re8 18. Bd6?!
18. Nxd5 I think it was time for White to take the pawn. The position of White's pieces can't really be improved.  )
18... Ne5 19. Bxd5 Nxd5 20. Nxd5 Bg4 21. Rd2?
21. Nc7 There was nothing wrong with this move.
21... Nd3 22. exd3 Bxd1 23. Rxd1 Bxd4 24. dxc4 Bxb2 25. Rb1 Bc3 26. Nxa8 Rxa8 27. Rxb7 Bxa5 28. c5 And White obtains an overwhelming advantage in this long and forcing line.  )
21... Red8! 22. Nb6 Rxd6 23. Nxa8 Nc6 Black now has some chances to survive.
24. Nf3 Rxd2 25. Nxd2 Bxb2 26. Rxc4 Bxe2 27. Re4 Bd3 28. Re3 Nb4? This move makes it easy for White.
28... Ne5! With Bd4 to follow. I have a feeling Black would still lose eventually, but it would have definitely been more of a fight.  )
29. Nb6 Bd4 30. Re7 The point. Once the rook becomes active, resistance is futile.
30... Nc6 31. Rxb7 Nxa5 32. Rd7 Nc6 33. Nb3 Bf5
33... Bxb6 34. Rxd3 And White should win easily.  )
34. Rxd4! Nxd4 35. Nxd4 A piece is a piece. So converted his edge into victory without any real trouble.
35... Bd3 36. Kg2 Kf8 37. Kf3 Ke7 38. Ke3 Bf1 39. Nf3 Kd6 40. Kd4 f6 41. Nd2 Be2 42. Nd5 f5 43. Nc3 Bh5 44. Nc4+ Ke6 45. f4 Kd7 46. Kc5 h6 47. Nd5 Ke6 48. Nc7+

Another very notable result was a victory by Harikrishna’s compatriot, Baskaran Adhiban, over Sergey Karjakin of Russia. Karjakin had played very solidly in the first four rounds,   while Adhiban had struggled. But in Round 5, Adhiban won with Black and he made it look easy.

Karjakin, Sergey vs. Adhiban, Baskaran
Tata Steel Masters | Wijk aan Zee, the Netherlands | Round 5 | 19 Jan 2017 | 0-1
8. Qd2 a6!? This move is becoming more popular.
8... O-O I've played this move twice in my games.  )
9. a3
9. dxc5 Nxc5 10. O-O-O This move looks more natural. White should castle long. Now if he does, the pawn on a3 is not especially well placed.  )
9... O-O 10. dxc5 Nxc5 11. Qf2
11. O-O-O b5 Black is threatening b4, after which he will have real counterplay.  )
11... Nd7 Strategically, this position is a disaster for Black, but he intends to change the course of the game by playing f6.
12. Nd4
12. Bd3  )
12... Nxd4 13. Bxd4 f6 14. exf6 Bxf6 15. Bxf6?! Helping Black develop his pieces.
15. O-O-O! White should have castled queenside. Then he would have been a bit better after:
15... e5 16. Bc5! Nxc5 17. Qxc5 exf4 18. Nxd5 White's pieces are very active.  )
15... Qxf6 16. g3 g5! Black attacks White's pawn structure.
17. O-O-O gxf4 18. Kb1?!
18. Rd4! This move would have given White decent prospects.
18... fxg3 19. Qxg3+ Kh8 20. Rh4 Rg8 21. Qh3 Nf8 22. Bd3 White has a dangerous attack for his sacrificed pawn.  )
18... f3! 19. g4?
19. Rd4 Once again, this move was best.  )
19... Ne5 20. g5 Qg7 Black is basically just up a pawn. Karjakin started throwing his pawns at Black and hoping for the best, but he is already pretty much lost.
21. g6?!
21. h4 Bd7 22. h5 Rf4 Black should win.  )
21... hxg6 22. Bd3 Bd7 23. Rdg1 Nxd3! 24. cxd3 Rf5 Black's king is totally safe, he is up two pawns, and the White knight cannot get to d4 to create some counterplay.
25. Rg4 Raf8 26. Rhg1 Be8 27. Nd1 Rh5 28. h4 Re5 29. Ne3 Bb5 30. Rd4 There are many ways for Black to convert his advantage, but I like how Adhiban closed out the game.
30... Re4!? 31. Rxg6
31. dxe4 Qxd4 32. Rxg6+ Kf7 33. h5 Qxe4+ 34. Ka1 Ke7 Black's king is quite safe in the center and his pawns can advance easily.  )
31... Bxd3+! The point. White resigned immediately.
31... Qxg6 32. dxe4 dxe4 And White's position is hopeless.  )

There was one more decisive result — a win by Radoslaw Wojtaszek of Poland over Loek van Wely of the Netherlands. Van Wely is having a terrible tournament, having now lost four of his five games.

In Round 6, I am looking forward to the game between So, who will have Black, against Adhiban. 

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Samuel Shankland is a United States grandmaster ranked No. 4 in the country. He is a professional player and recipient of the Samford Fellowship in 2013, the most prestigious award in the United States for young chess players. He was also a member of the team that won the gold medal at the 2016 Chess Olympiad. He is at @GMShanky on Twitter, has his own site, and is also on Facebook.