The first round after the break produced three decisive games, but no change in the overall leader as Wesley So won again.

There were several exciting games in Round 6 of the elite section of the London Chess Classic and three of them ended decisively. The most important results were that Wesley So of the United States, the overall tournament leader, won again, while Hikaru Nakamura, his compatriot, lost. That may mean that the battle for the overall winner of the Grand Chess Tour — the season-long series of tournaments for which the London Classic is the capper — may be effectively decided and that So has won. Nakamura had stood the best chance of overtaking So, but he needed to win the London Classic and have So finish no better than fourth, and neither of those things seems likely anymore.

So’s victory came over the increasingly hapless Veselin Topalov of Bulgaria, who lost his fifth game of the event. He played a really lousy game against So, making several big mistakes while not using much of his time. He was basically dead lost after just 18 moves, and that despite playing White.

Topalov, Veselin vs. So, Wesley
London Classic | London | Round 6 | 15 Dec 2016 | 0-1
d5 18. Be2? A terribly passive square for the bishop. Topalov played this move after thinking for four minutes. I have no idea what he had in mind.
18. Bd3 After this move, chances would be about equal.
18... Qg5 19. Nb3 f5 20. exf6 Nxf6 21. Qc1 White is fine  )
18... Qg5 This is totally forced and gives Black a winning position. White can do nothing as Black plays f5 and f4.
19. a5
19. Nb3 f5 20. exf6 Rxf6 With the bishop on d3, White would have good play with Re1. As it is, his pieces are blocked and passive and Black threatens Rh6 followed by Qh5.  )
19... f5 20. exf6 Nxf6 21. Ra4 Black has no shortage of winning moves. Basically anything that brings rooks to the h-file will do the trick.
21... Rf7 Also threatening Nh5 since Bxc7 is no longer possible.
21... Kg7 This move would probably also have been enough for Black to win.  )
22. Re1 Nh5! What to do about the bishop on g3? White's position falls apart rapidly.
23. Bxg4 Nxg3 24. Re8+ Kg7 25. Rxc8 Bxf2+ 26. Kh2 Qe5 27. Kh3 Ne2

So now has 4.5 points and is a half point ahead of Fabiano Caruana, who aided him in his quest for the Grand Chess Tour title by beating Nakamura.

It was a very nice victory for Caruana as he outprepared Nakamura, who is now his teammate. The win gave Caruana 4 points, while knocking Nakamura back to an even score. Nakamura has now lost both of his games to the supertalents who transferred to the American federation to help it win the gold medal at the 2016 Chess Olympiad.

Caruana, Fabiano vs. Nakamura, Hikaru
London Classic | London | Round 6 | 15 Dec 2016 | 1-0
13. g4 g5!? This is a common idea in this opening. Black is content leaving his king in the center and tries to use his g-pawn to secure the e5 square for a knight. But Caruana came prepared with a new plan.
14. h4! gxf4 15. Be2 b4!?
15... Rg8 Was the move once played by Maxime Vachier-Lagrave in this position, but this also is no bed of roses for Black after:
16. g5! hxg5 17. hxg5 Ne5 18. Qxf4 Nfd7 19. Be3 Bxg5 20. Qxg5 Rxg5 21. Rh8+! Nf8 22. Bxg5 And White has a fierce attack.  )
16. axb4 Ne5 17. Qxf4 Nexg4 18. Bxg4 e5 19. Qxf6 Bxf6 20. Nd5 Qd8 Up to here Hikaru was playing very quickly, suggesting that he had prepared this line before the game. But he must have not seen White's next move in his preparation.
21. Nf5! At first, the computer engine does not understand this move, but after it runs for long enough, it says White is much better.
21. Nc6 This natural and forcing move is the computer's top choice at first, but after
21... Bxg4 22. Nxd8 Bxd8 I think Black should be fine.  )
21... Rb8 Not the best, but Black was in big trouble anyway.
21... Bxf5 22. Bxf5 Rb8 23. Kb1 The longer the computer runs, the poorer its evaluation of Black's position becomes. Black has no active play at all and a lot of weaknesses. White's two pieces are better than the queen.  )
22. Nxf6+ Qxf6 23. Rxd6 Not a bad move of course, but White had better.
23. Nxd6+! Was even stronger.
23... Kf8 24. Bf5! The point. It's possible Caruana missed this move. White can follow with Bc5 and Black's troubles will deepen.  )
23... Be6 24. Rhd1 O-O 25. h5! Qg5+? Black cannot survive this.
25... Rfe8! This move was much more resilient. White would then have to maintain the tension with a patient move since a direct assault doesn't really work:
26. Bh4 Qh8 27. Ne7+ Rxe7 28. Bxe7 Bxg4 29. Rd8+ Rxd8 30. Rxd8+ Kh7 31. Rxh8+ Kxh8 32. Bf6+ Kg8 33. Bxe5 Bxh5 Black should be able to hold a draw in this endgame.  )
26. Be3! Qf6
26... Qxg4 27. Nxh6+  )
27. Nxh6+ Kh8 28. Bf5 Black is practically in stalemate.
28... Qe7 29. b5
29. Nxf7+ Rxf7 30. Rxe6 Qxb4 31. Rh6+ Kg7 32. Rg1+ Kf8 33. Rh8+ Would be a similar continuation to the game.  )
29... Qe8 30. Nxf7+! Rxf7
30... Qxf7 31. Rxe6 This move offers no salvation either as Rh6+ will soon follow.  )
31. Rxe6 Qxb5 32. Rh6+ Black resigned in view of
32... Kg8 33. Rg1+ Kf8
33... Rg7 34. Be6+ Kf8 35. Rh8+ Ke7 36. Rxg7+ Kxe6 37. Rh6#  )
34. Rh8+ Ke7 35. Rxb8! Qxb8 36. Bc5+ And Black is either mated or loses his queen.
36... Kd8
36... Kf6 37. Rg6#  )
37. Rg8+ Kc7 38. Rxb8

The final decisive result of the day was the win by Maxime Vachier-Lagrave of France over Levon Aronian of Armenia, who suffered a strange meltdown in a level position.

Vachier-Lagrave vs. Aronian, Levon
London Classic | London | Round 6 | 15 Dec 2016 | ECO: C50 | 1-0
1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O Nf6 5. d3 O-O 6. a4 a5 7. c3 d5 8. exd5 Nxd5 9. Re1 Bg4 10. Nbd2 Nb6 11. Bb5 Bd6 12. h3 Bh5 13. Ne4 f5 14. Ng3 Bxf3 15. Qxf3 Ne7 16. Bg5 c6 17. Bc4+ Nxc4 18. dxc4 e4 19. Nxe4 fxe4 20. Qxe4 Rf7 21. Rad1 Qc7 22. Rxd6 Qxd6 23. Bxe7 Qd2 24. Bc5 h6 25. Qe2 Rd8 26. Bd4 Qg5 27. Qg4 Re7 28. Rxe7 Qxe7 29. Qf5 Re8 30. Qxa5 Qf7 31. Kh2 This position is around equal. White has three pawns for the exchange but he will shortly lose one of them, leading to a material balance where neither side has any weaknesses.
31... Qf4+?! Objectively, Black is still fine, but now he has to play accurately.
31... Qxc4 Why not take the pawn?  )
32. g3 Qf7
32... Qf3 33. Qc7 And Black does not have time to play Re1.  )
33. Kg2 Re1?! Why?
33... Qxc4 Again, restoring the material balance should lead to a position of roughly equal chances.  )
34. g4 Rd1? Black is now clearly worse.
35. Qe5! White's centralized queen dominates the board, he will keep all three pawns for the exchange, and Black has no counterplay.
35... Qg6 36. b4 b6? I'm not sure what Aronian overlooked in this position.
36... h5 White should still win, but Black can still fight on.  )
37. Bxb6! Calling Black's bluff.
37... c5
37... Rd3  )
37... Qd3 38. Bd4 Qf1+ 39. Kg3 Black is not threatening mate or anything even close.  )
38. Bxc5 Qc6+ 39. f3 Rd3 40. Qb8+ Kh7 41. Qf4 Now with five pawns for the exchange, Black has no reason to continue to play.

I think that the most interesting game to watch in Round 7 will be between Anish Giri of the Netherlands and Topalov. Giri has drawn all his games, but he might try to play more aggressively to take advantage of whatever is wrong with Topalov. 

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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 and is also on Facebook.