I think I may have found an improvement in the game Svidler-Yifan which was analyzed in the October 2009 Chesspub update.  

(1) Svidler,Peter (2739) - Hou,Yifan (2584) [C11]
NH Chess Tournament Amsterdam, NED (1), 20.08.2009


1.e4 e6 2.d4 d5 3.Nc3 Nf6 4.e5 Nfd7 5.f4 c5 6.Nf3 Nc6 7.Be3 Be7 8.Qd2 0-0 9.Be2 a6 
0-0 b5 11.a3 Qb6 12.Nd1 a5 13.c3 Bb7 14.Bf2 f6 15.exf6 Nxf6 16.dxc5 Bxc5 17.Bxc5 Qxc5+ 18.Qe3 Qxe3+ 19.Nxe3 b4 20.axb4 axb4 21.cxb4 Nxb4 22.Nd4 Kf7 23.Ng4 Rxa1 24.Rxa1 Ra8 25.Rxa8 Bxa8 26.Ne5+ Ke7 27.Kf2 Bb7 28.Ke3 Ba6 29.Bf3 Bc8 30.Kd2 Na6 31.Kc3 Nc5 32.b4 Nce4+ 33.Kd3 g5 34.g3 gxf4 35.gxf4 Kd6 36.Nb5+ Ke7 37.Nd4 Kd6 38.Nb5+ Ke7 39.Kd4 Bb7 40.Nc3 Nxc3 41.Kxc3 Kd6 42.Be2 Nd7 43.Nf7+ Ke7 44.Ng5 h6 45.Nf3 Kf6 46.Kd4 Kf5 47.Ne5 Bc8 48.Bb5 Nf6 49.Ke3 Ng4+ 50.Nxg4 Kxg4 51.Bc6 d4+ 52.Ke4 d3 53.Ke3 d2 54.Bf3+ Kh3 55.b5 Bb7 56.Bd1 Kxh2 57.Kxd2 Kg3 58.Ke3 Kh4 59.Bf3 Bc8 60.b6 Kg3 61.b7 Bxb7 62.Bxb7 Kg4 63.Ke4 Kh5 64.Ke5 1-0


Based on my analysis with Rybka, on black’s 18th move, instead of exchanging queens I think it would have been better to play 18...Ne4. For instance, if black were to exchange queen’s now, then I think the knight would be better placed on c5 than on f6, and would e.g. have nasty forks on d2 (via b3) in some lines. And as well, the rook is now attacking the f4 pawn and white would have to spend a move addressing that. I’m sorry I don’t have a diagram. I tried the links in the discussion forum but they didn’t work on my server. 

I’ve spent the past couple months analyzing this with Rybka 3, often leaving my engine running while I was at work, and I’m pretty confident black can hold this position - but there’s always some doubt. I also think that both sides had played very well up to this point. I prefer Yifan’s 13...Bb7 to 13...a4 but that’s my opinion (based on my analysis with Rybka, though).

Some of Rybka’s main lines that I’ve recorded from this position are the following:

A)      19.Nd4 Nxd4 20.cxd4 Qb6 21.Bg4 Rac8 22.Nc3 Kh8 23.Rfe1 Rc7 24.Rac1 Rfc8 25.Red1 b4 26. axb4 axb4 27.Nxe4 dxe4 28.Rc5 g6 29.Rdc1 Bd5 and I don’t see how White can make progress here.

B)      19.Qxc5 Nxc5 20.g3 b4 (or 19.g3 b4 20.Qxc5 Nxc5) 21.Re1 bxa3 22.Rxa3 Ba6 23.Bxa6 Rxa6 24.b4 axb4 25.Rxa6 Nxa6 26.Rxe6 Rf6 27.Rxf6 gxf6 28.cxb4 Naxb4 and I think White can hold this Knight and Pawn endgame.

C)      19.Qxc5 Nxc5 20.Bxb5 Nb3 21.Rb1 Rxf4 22.Nf2 Rxf3 23.gxf3 Ne5 24.Nh3 Nd2 25.Ng5 Nxb1 26.Rxb1 Ba6 27.Ba4 Rf8 28.Re1 Nd3 29.Rxe6 Nxb2 30.Be8 Bc8 31.Re7 h6 and so on, with black holding.

If anyone has some further input into this move that would be cool.