With a surge of 4.5 points on Day 2 of the competition, Ivanchuk is now the sole leader.

Anton Korobov, the leader after Day 1 of the World Rapid Championship faded on Day 2, falling into a tie for fourth. But one of his compatriots, Vassily Ivanchuk, replaced him at the top of the leaderboard after scoring 4.5 points in five rounds.

Ivanchuk now has 8 points after 10 rounds. Shakhriyar Mamedyarov of Azerbaijan, who lost to Ivanchuk in Round 10, and Ian Nepomniachtchi of Russia, trail Ivanchuk by half a point. Seven other players, including the defending champion, Magnus Carlsen of Norway, who was beaten by Ivanchuk in Round 8, are a further half point back. 

The Rapid Championship, which is being held in Doha, Qatar, is 15 rounds over three days and has a prize fund of $200,000, with $40,000 for first. 

Korobov was knocked from the lead in Round 6 when he lost to Levon Aronian of Armenia. 

Aronian, Levon vs. Korobov, Anton
World Rapid | Doha, Qatar | Round 6 | 27 Dec 2016 | 1-0
38. Kxe3 Kf7?! A step in the wrong direction
38... c4 Black should be able to easily hold a draw in this position because White does not win the pawn on e4.
39. Kxe4 c3 40. Bc1 Bxe2  )
39. Kxe4! Bxe2?
39... c4 After this move, I think that Black would still be able to hold a draw.
40. bxc4 Bxc4 41. Kf3 g6 42. e4 h5 And Black should be able to construct an opposite-colored bishop fortress since White cannot create connected passed pawns without a ton of exchanges. For example:
43. f5 Ba6 44. Kf4 Bb7 45. h3 Bc6 46. g4 hxg4 47. hxg4 Bb7 48. e5 gxf5 49. gxf5 Bc8 And Black draws by playing Bc8 and Bd7.  )
40. Kd5 White will win both queenside pawns and have a passed pawn on both sides of the board. Black should lose.
40... Bd1 41. Kc4 g6 42. Bc1 Ke6 43. Be3 Kf5 44. Bxc5 Kg4 45. Bxb4 Kh3 46. Be1 Kxh2 47. b4 Bf3 48. b5 Kg2 49. b6 h5 50. Kc5 Kf1 51. Bc3 Kg2 52. Be5 Kh3 53. Kd6 Kg4 54. Ke6 Be4 55. Bd6 Bf5+ 56. Ke7 Be4 57. Kd8

Aronian’s win vaulted him into first, but his standing atop the leaderboard was short-lived as he scored only a half point in the next two games, including a loss to Mamedyarov in Round 8. With the victory, Mamedyarov took over the top spot in the standings. 

Aronian, Levon vs. Mamedyarov, Shakhriyar
World Rapid | Doha, Qatar | Round 8 | 27 Dec 2016 | 0-1
a4 14. Rfe1?! The start of a bad plan.
14... axb3! 15. axb3 Ra2! White has trouble holding his position together here since Ra1 is not possible.
16. exd5
16. Ra1 Rxa1 17. Rxa1 dxc4  )
16... cxd5 17. Rxe6 Presumably this was Aronian's plan when he played Rfe1, but Black's pieces are too active for it to work.
17. c5 Nc6  )
17... fxe6 18. Bh3 Qb6! 19. Re1 e5! 20. cxd5
20. dxe5 dxc4 and Black has a huge edge.  )
20... Qxd4! Forcing an exchange of queens after which Black will simply be up an exchange. Mamedyarov should won easily.
21. Bxd4 Rxd2 22. Be3 Rd3 23. Be6+ Kh8 24. Nf3 Na6 25. Rc1 Nb4 26. Rc5 b6 27. Ng5 h6 28. Nf7+ Kh7 29. Rb5 Nc2 30. Bxb6 Rb8 31. Bd7 e4 32. Bd8 Rxb5 33. Bxb5 Kg8 34. d6 exd6

Mamedyarov held onto the through Round 9 by beating Korobov. But he was then outplayed and beaten by Ivanchuk.

Ivanchuk, Vassily vs. Mamedyarov, Shakhriyar
World Rapid | Doha, Qatar | Round 10 | 27 Dec 2016 | 1-0
37. Rb3 This is a difficult position for Black, but he can hold on with precise play. But this is very hard to do in a complicated endgame with little time on the clock.
37... Rc1?
37... Ne2+! 38. Kg4 Rd5! And Black would be fine. White has a hard time coordinating his pieces; the rook on b3 looks really silly, for example.
...   )
38. Kf4! The White king penetrates and his d-pawn will become far more dangerous than it looks. With precise calculation, Black could advance his pawns, but White would still be much better.
38... a4 39. Rb2
39. Rb4? Nd5+  )
39... b4! 40. axb4
40. Rxb4? Nd5+  )
40... a3 This position looks very scary for White, but he is doing well. I'm sure Ivanchuk had calculated this before he played Kf4.
41. Rd2! Nb5 A sad necessity, but now a2 is no longer a Threat.
41... a2 Black's pawn is not quite fast enough.
42. d7+ Kd8 43. Nc6+ And White promotes his pawn first.  )
42. Ke5 Kd8 43. Na6?
43. Ke6 This move was more accurate.  )
43... Rb1?
43... Rh1! By some miracle Black is holding on, but this is almost impossible to calculate in a rapid game.  )
44. d7 Rb2 45. Rd5! Rxf2 Black resigned instead of waiting for Nc5
45... a2 46. Nc5 a1=Q White is very fortunate that the rook on b2 prevents check.
47. Ne6+ Ke7 48. d8=Q+ Kf7 49. Qf8#  )

One thing I like about the rapid time control is that it can punish slow players. A couple times on Day 2, players with huge advantages faltered because of getting into time pressure. It was a good reminder that time management is part of chess, too. That is something that Zdenko Kozul of Croatia was reminded of in his Round 10 game against Sandro Mareco of Argentina.

Kozul, Zdenko vs. Mareco, Sandro
World Rapid | Doha, Qatar | Round 10 | 27 Dec 2016 | 0-1
Bc6 White has a huge advantage and should be able to win easily, but, in time pressure, he begins to make mistakes.
51. Qc3
51. Ba3! This move looked rather effective.
51... Qxa3 52. Qf6+ Ke8 53. Qf7+ Kd8 54. Ne6+ Kc8 55. Qc7#  )
51... Ke8 52. Ba2 Rf8 53. Ba3 Qe2 54. Qe3+? Panicking and letting Black escape into an ending in which both sides have chances. There was no need to allow this.
54. Bb3 Simple and easy White prevents Qxa2 and Qd1+ after which Black should lose.  )
54. Bxf8 Even this move should win -- White wins material and Black has no major threats.
54... Qd1+ 55. Kh2 Qh1+ 56. Kg3 Qg2+ 57. Kf4  )
54... Qxe3 55. fxe3 Rh8 Black's chances are not worse, and, after further mistakes by White, he even goes on to win.
56. Bf7+ Kd8 57. Bxg6 Rxh4 58. Bxf5 Rxa4 59. Bd6 Ra1+ 60. Kf2 Rd1 61. Bc5 a4 62. e4 Rc1 63. Bb6+ Ke8 64. Ke3 a3 65. Be6 Bb5 66. Kd4 Rc2 67. Bf7+ Kd7 68. e5 a2

Rapid chess also produces gorgeous checkmates that are seldom seen in slow chess. I quite enjoyed this simple but brutal one executed by Alexander Moiseenko of Ukraine against Pavel Tregubov in Round 8:

Tregubov, Pavel vs. Moiseenko, Alexander
World Rapid | Doha, Qatar | Round 8 | 27 Dec 2016 | 0-1
22. Rxd5 Qh3! Black was much better, but White's last move was a terrible that immediately leads to defeat. The threat of Rg6 on the next move is decisive no matter which piece White takes. He resigned instead of facing
23. gxh3
23. gxf3 Rg6+ 24. Kh1 Qxf3#  )
23... Rg6+ 24. Qg4 fxg4 And White cannot prevent both gxh3# and Bxd5.

There is only one more day of competition and it will start with Ivanchuk facing Nepomniachtchi in Round 11. With five rounds to go, the tournament is still far from decided and it should be an exciting finish.

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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.