China, the defending champion, was beaten by Ukraine. Azerbaijan also lost. There are now only three unbeaten teams left in the open section.

More teams were knocked from the ranks of the unbeaten in Round 5 of the 42nd Chess Olympiad in Baku, Azerbaijan. The most prominent was China, the defending champion, which lost to Ukraine. 

Only three teams – Ukraine, India and the Netherlands — remain undefeated in the open section,  while only two teams – Ukraine and Russia - have perfect match scores in the women’s group

Ukraine’s victory over China was by the slimmest of margins, 2.5 points to 1.5. Three of the games were hard-fought draws, but on Board 3, Yuriy Kryvoruchko beat Yu Yangyi, who is higher rated, using an unusual opening idea. In the English Attack in the Najdorf Sicilian, both sides typically castle on opposite sides of the board. But instead of castling queenside, Kryvoruchko played a4 and started playing for a strategic edge on the queenside.

Kryvoruchko, Yuriy vs. Yu, Yangyi
42nd Olympiad Open 2016 | Baku AZE | Round 5.3 | 06 Sep 2016 | ECO: B90 | 1-0
b5 0-0 is a slightly more common move order for Black. But I don't think Yu Yangyi expected White to play:
11. a4!? While unusual, this move has been played in a number of previous games
11... bxa4 12. Rxa4 O-O 13. Na5! Nb8 14. g5 Ne8 15. Nd5 White is dominating the position on both sides of the board!
15... Bxd5 16. exd5 Qd7 17. b3 Bd8 18. Bd3 f5 19. f4 Keeping Black's counterplay to a minimum.
19... exf4 20. Bxf4 Qf7 21. O-O Nd7 22. Be3 Bxa5 23. Rxa5 Qh5 24. Rxa6 Rxa6 25. Bxa6 White is simply up a pawn. Black has a small amount of compensation, but he wasn't able to put up much resistance:
25... Ne5 26. Be2 Qg6 27. Kh1 h6 28. gxh6 Nf6 29. Bf4 Ne4 30. Qd4 Re8 31. Rg1 Ng4 32. Bxg4 fxg4 33. Qxg7+ Qxg7 34. hxg7 Rc8 35. Rg2 Ra8 36. Re2 Nc3 37. Re1 Nxd5 38. Bxd6 Rd8 39. Be5 Nb4 40. Bf6 Rb8 41. c3 Nd5 42. Bd4 Nf4 43. Re4

The host team from Azerbaijan had been another one of the undefeated teams before Round 5, but it was beaten rather convincingly by India by a score of 3-1. The crucial game was the matchup on the top board between Shakhriyar Mamedyarov and Pentala Harikrishna. Mamedyarov played an interesting new opening idea, but Harikrishna was up to the task in the complicated position that emerged on the board. The turning poing was Harikrishna’s visually pleasing exchange sacrifice:

Mamedyarov, Shakhriyar vs. Harikrishna, Pentala
42nd Olympiad Open 2016 | Baku AZE | Round 5.1 | 06 Sep 2016 | ECO: D43 | 0-1
18. Qf3 It had been a very complicated game up to this point. White had played a new move in this position and gained a tangible initiative so I think that Mamedyarov probably felt quite confident about his prospects.
18... Rd5! A great practical idea! White can win the exchange, but giving up the light-square bishop doesn't seem like a good idea. However, if White does not take the rook, he has a problem as Black is threatening Rxe5. The other virtue of Black's move is that he has also stopped Whites attack against the pawn on c6.
19. Qg4 Kf8 20. Bxd5 This was probably a very tough decision for Mamedyarov. Objectively White's probably doing well, but his position suddenly seems a lot riskier.
20. Bf4 Would have been a reasonable move when the position would have been quite complicated.  )
20... exd5 21. Ra4!? This move might look completely useless, but Mamedyarov wants to open the a-file. If he is successful, that looks like it could be very dangerous for Black as the rook on h8 would be too far away to aid in the defense. But is it really that far?
21... c5 22. Ba3 Rh6!! The rook lift allows Black to shore up his defenses.
23. Bxb4 axb4 24. Rfa1 Qe8 25. Ra7 Qc6 26. Qg5 Re6 The Black rook is just in time to help.
27. Qd8+ Re8 28. Qd6+ Kg8 The computer thinks that White is better here, but practically, Black's constant threats because of his passed pawns give him the initiative.
29. Rxb7 An attempt to simplify the position and salvage a draw.
29. f4 d4! 30. Qxc6 Bxc6 31. Rc7 c4! is probably what Mamedyarov overlooked. The Black pawns roll down the board quickly!
32. bxc4 b3  )
29. Qxc6 Bxc6 now Black's threat of playing c4 make White's life miserable.  )
29... Qxb7 30. Qxc5 Rxe5 31. Ra7 d4! Mamedyarov probably missed this move in his calculations.
32. Qxd4 Rd5! Now it is all over.
33. Rxb7 Rxd4 34. Kg2 Rd1
34... Rd1 35. Rc7 Rb1 and after Black wins the White b-pawn, his b- and c-pawns would be too strong.  )

On Board 3, Vidit Gujrathi completely controled the game to score his fifth win of the competition, this time against the latest addition to the Azeri team, Arkadij Naiditsch. (Naiditsch played for Germany until the previous Olympiad.)

On paper, the Netherlands had an easier path to join the ranks of the unbeatens as it played Belarus, the No. 23 seed. But this turned out to be a crazy match that could have gone either way. On the top board, Anish Giri of the Netherlands, got into serious trouble against Sergei Zhigalko. But Zhigalko missed the best continuation and Giri was able to survive.

The match was decided by a completely insane, but hugely entertaining, tactical fight on Board 4 between Kirill Stupak of Belarus and Benjamin Bok of the Netherlands. White played an absolutely strange opening – voluntarily moving his king to e3. He soon had a terrible position, but his bravery almost paid off when Bok sacrificed a bit too much to get at White’s king. Then the game turned around once more at the end:

Stupak, Kirill vs. Bok, Benjamin
42nd Olympiad Open 2016 | Baku AZE | Round 5.4 | 06 Sep 2016 | ECO: D43 | 0-1
Kh8 28. Rd1?
28. Bg2! was a surprisingly easy and effective defensive idea. Then White could play Kf1 and the White king would be completely safe. Black would just be down a rook.  )
28... Re8+ 29. Kd2 Bxf3 30. Qxf3? d3! This was obviously what White missed in his calculations. The floodgates have been opened and the White King has nowhere to hide.
31. Rb1
31. Qxd3 Qxb2+ 32. Qc2 Bxb4+! 33. Kd3 Qa3+ 34. Kc4 b5+ 35. Kxb5 Qa5+ 36. Kc4 Rc8+ and Black's winning easily.  )
31... Bxb4+ 32. Kxd3 Qe6! and Qb3+ is a huge threat.
33. Kc2 Rc8+ 34. Qc3+ Bxc3 35. bxc3 Qc6

There was also a curious study-like position in the match between England and Vietnam. According to the engine assessments, in the following game, the top Vietnamese player, Le Quang Liem, appeared to miss an elementary win against Michael Adams. But upon deeper inspection, Black actually has an amazing draw that even the computer missed at first:

Le, Quang Liem vs. Adams, Michael
42nd Olympiad Open 2016 | Baku AZE | Round 5.1 | 06 Sep 2016 | ECO: D55 | 1/2-1/2
1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Be7 5. Bg5 h6 6. Bh4 O-O 7. e3 Nbd7 8. Rc1 c5 9. dxc5 dxc4 10. Bxc4 Nxc5 11. O-O Nfe4 12. Nxe4 Nxe4 13. Bxe7 Qxe7 14. Qd4 Nf6 15. Bb3 b6 16. Qf4 Bd7 17. Rc7 Rfc8 18. Rd1 Rxc7 19. Qxc7 Qd8 20. Qxd8+ Rxd8 21. Ne5 Kf8 22. Ba4 Ke8 23. Bc6 a5 24. Kf1 Bxc6 25. Rxd8+ Kxd8 26. Nxc6+ Kc7 27. Ne5 Nd5 28. Ke2 f6 29. Nf3 Kd6 30. a3 f5 31. Kd3 Nc7 32. Nd4 Kd5 33. f3 a4 34. e4+ fxe4+ 35. fxe4+ Kc5 36. h4 h5 37. g3 b5 38. Kc3 Kd6 39. Kb4 Ke5 40. Nxb5 Nxb5 41. Kxb5 Kxe4 42. Kxa4 e5 43. b4 Kf3 44. b5 e4 45. b6 e3 46. b7 e2 47. b8=Q e1=Q 48. Qf4+ Kg2 49. Kb5 Qe2+ 50. Ka5 Qe1+ 51. Kb6 Qb1+ 52. Ka7 Qh7 53. Kb8 Qb1+ 54. Kc8 Qc2+ 55. Kd7 Qd3+ 56. Qd6 Qb5+ 57. Ke7
57. Qc6+ appears to win instantly, and the computer thinks so, too, but these players aren't so bad. They saw something the computer did not:
57... Qxc6+ 58. Kxc6 Kxg3 59. a4 Kf2!! If g5, then hxg5, and the White pawn will promote to a queen on g8 with check.
60. a5 g5 61. a6 hxg5 leads to a queen and pawn vs queen endgame which is a theoretical draw, although it is not so easy to prove in practice.
61... gxh4 62. a7 h3 63. a8=Q h2 64. Kd6 Kg1 Without the pawn on h5, this is a theoretical draw. But even with the pawn there, it doesn't seem like White has any way to force a win.  )
57... Qb7+ 58. Ke6 Kh3 59. Qd3 Qc6+ 60. Qd6 Qb7 61. Kf5 Qf3+ 62. Kg6 Qg4+ 63. Kf7 g5 64. hxg5 Qxg5 65. a4 Qf5+ 66. Ke7 Qh7+ 67. Kd8 Qg8+ 68. Ke7 Qh7+ 69. Kf6 h4 70. gxh4

The English players handled themselves nicely on the other boards and won the match, 3-1.

After back-to-back draws, Magnus Carlsen, the World Champion, got back on the winning track against Luc Winants of Belgium. Norway, Carlsen’s team, followed suit, winning the match, 3-1. 

In the women’s section, the other World Champion, Hou Yifan, recovered from her headline-grabbing loss in Round 4 to win in the style of 19th century attacking genius Paul Morphy:

Hou, Yifan vs. Zimina, Olga
42nd Olympiad Women 2016 | Tromso NOR | Round 5.1 | 06 Sep 2016 | ECO: C65 | 1-0
c6? The last move seems innocuous enough, but
10. dxe5 dxe5 11. Nd5!! Opens the center by force.
11... cxd5 12. exd5 Bxb5 13. Nxe5 h6 14. Bxf6 Qxf6 15. Ng4+ Black's completely lost. The rest is easy.
15... Qe7 16. Qd4 Be2 17. Qxh8 Nd7 18. Qc3 f5 19. Rxe2 Qxe2 20. Re1 Qxe1+ 21. Qxe1+ Kd8 22. Ne5 Nxe5 23. Qxe5 Rc8 24. c3

Hou’s win helped China to a comfortable 3-1 victory over Italy.

Russia continued to steamroll their opponents crushing a strong, but inexperienced, team from Kazakhstan, 3.5 - 0.5.

Ukraine won a tough match against Serbia to join Russia in the lead. Ukraine was led by the strong Muzychuk sisters. The younger sister, Anna, won on Board 1 with a beautiful tactical idea against Jovana Rapport (the wife of Hungary’s top player, Richard Rapport):

Rapport, Jovana vs. Muzychuk, Anna
42nd Olympiad Women 2016 | Tromso NOR | Round 5.1 | 06 Sep 2016 | ECO: B38 | 0-1
19. b3 White seems to have things under control, especially if she can play hxg6 and Bh6. But Muzychuk finds a way to make White's King feel uncomfortable as well.
19... f5! 20. h6 fxg4! 21. hxg7 gxh3 22. gxf8=Q+ Rxf8 White is up a piece, but dealing with the h3-pawn isn't easy.
23. f4 Jovana probably thought that she could play Bf3 next and then she could keep the h-pawn in check.
23... Nxe4!! 24. fxe5 h2! An unexpected intermediate move!
25. Qd4
25. Bf3 Nxd2! 26. Kxd2 Bxf3  )
25... h1=Q+ 26. Bg1 Rf2 It is all but over; White cannot safe herself.
27. Nxe4 Qxg1+ 28. Kd2 Rxe2+

On Board 2, Mariya, the former World Champion, won a more positional game against Irina Chelushkina to seal Ukraine’s victory.

Ukraine has clearly emerged as a team to beat in both sections. Their men’s team has already beaten two of the most feared teams in the Olympiad – Russia and China. In Round 6 on Thursday, Ukraine will be put to test again as it faces the star-studded American team, which features three of the top 10 players in the world.

India has also been amazingly consistent. Every player on the team appears to be in excellent form, which is what a team needs if it is to win the Olympiad. In Round 6, India will face the surprising joint leaders, the Netherlands, in a match that could decide which team takes sole possession of first.  

In the women’s section, Russia has been dominating its opponents. In Round 6, the women will have a chance to avenge the loss of the men’s team when they take on Ukraine, with the possibility of becoming the sole leader of the tournament at stake. 

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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 about to start his junior year at Stanford University. He can be found on Twitter at @parimarjan.