Hesam7: <sleepkid: Actually it would appear that Simagin found the improvement 10. Qe2, achieved a winning position, but then blundered the game away, as this is a victory for Korchnoi.>
A great deal of mistakes by both sides in this game. Korchnoi's opening was a disaster, then White started playing badly from an overwhelming position:
<18. Nd5?> This squanders a great deal of White's advantage. 18. Na4! practically wins:
18. ... f5 is met with the simple 19. exf5 gxf5 20. Rac1.
18. ... Rfd8 19. Qe3! (19. Rac1 seems more natural but White is planning to double the rooks on the d-file) 19. ... Bf8 (defending against Nc5) 20. Rd4 with Rad1-b3-g3-f4 to follow. Black is completely strangled.
18. ... Qe5 19. Rac1 Bxe4 20. Rc5 Qf4 21. b3 Bb7 22. Rc4 Qb8 23. Nc5 and with Qe7 & Ne6 coming Black is toast.
18. ... Qg5 19. h4! Qe5 (19. ... Qxh4? 20. Nc5) 20. Rac1 transposing to the previous line but with an extra move for White .
<21. Ng5?> Now White has no advantage whatsoever. Much better was 21. Rac1 fxe4 (the other two captures lose the bishop!) 22. Rc5! Qf6 23. Rc7 Rb8 24. Qe3 Ba8 25. Rdc1 and Black's defenses are breached.
<25. fxe3?> The losing move, 25. Bh3 defending g2, was the only defense.
<27. Kxg2?> This will lose very quickly, 27. Rd2 was the toughest defense. The game might have gone as follows: 27. ... Ba8 28. Bh3 Bh6 29. Re1 Bf4 30. Qd3 Bxh2+ 31. Rxh2 Qg3+ 32. Rg2 Qxe1+ 33. Kh2 Kg7 34. Qd4+ Kh6 35. Qd2 (35. e4 Rf4; 35. Qd6 Rf1) 35. ... Qh4 36. e4+ Qf4+ 37. Qxf4 Rxf4 38. Kg3 Rxe4 39. Rd2 Kg5.
<29. ... Qh4?> Black misses a quick win: 29. ... Be5! 30. Rd4 Qf6! (30. ... Rxh2+?! 31. Kg1 Qh4 [31. ... Qf6? 32. Rf4! =] 32. Qg8+ Kxg8 33. Be6+ Kg7 34. Rxh4 Rxh4 35. Rc1 Bxb2 36. Rc7+ Kf6 in this rook and opposite colored bishops ending Black is 2 pawns up but there is still a lot of work to be done) 31. Qf7 Qxf7 32. Rd8+ Kg7 33. Rd7 Rxb2! 34. Rxf7+ Kxf7 we still get the same kind of ending but here White will lose his a-pawn because of zugzwang. For example: 35. h3 a5 36. Kg1 Ke7 37. Bd1 Rd2.
<30. Bh3??> Now Black is completely winning again. The immediate 30. Rd8+ Qxd8 31. Qe6 was much better since Black has not played ... Be5.
<34. ... Qxe3??> This gifts White a perpetual. After 34. ... Rh1+ 35. Ke2 Rxa1 White has a check or two but that is it.
<37. Qf8+??> A fitting end to this comedy of errors. White could have forced a draw with Qh4-Qe7.