Material: Down N for R, so Black must do more than gain an exchange to win. The White Kb1 is vulnerable to back-rank mates. The Black Pb4 and Pc3 are coordinated in attacking the dark squares around the White Kb1, backed by Qa5 and Nc5. The Black Nf6 defends Kg7 and attacks Rd5. The Black Rh8 requires activation. The capture 32…Nxd5 is an obvious candidate.

Candidates (32…): Nxd5, Re8, b3

32…b3 (threatening 33…Qxa2+ 34…Qa1#)

Because 33.Qxc3 Qxc3 34.bxc3 Nxd5 is an obvious loss for White:

(1) 33.axb3 [cxb3 appears worse] Nxd5

With the clearance sacrifice 32…b3, 34.Qd4 is now a decisive loss for White.

(1.1) 34.Qd4 Ng4 35.Qxc3 [Qc4+ d5]

35...Qxa2+ 36.Kc1 Qa1+ 37.Kd2 Qxg1 38.Qxb4 Re8

White has little to play for.

(1.2) 34.Qg5 Ng4

and after 35…Ke8, the Black K can endure Re1+ and runs for cover on the Q-side. The threat of a forced mate becomes paramount when the checks run out.

Time to peek. I found the clearance sacrifice 32…b3 fairly rapidly, but the tangle of variations made precise enumeration impossible. The point is that eventually Black finds harbor for his K with a material lead.

32...b3 33.axb3 <cxb2> 34.Kxb2 Nxd5

Hi, <Once> and <lost in space>. With the Qs off, the position is a draw as follows. The Black N must hold the K-side Ps, leaving the White K free to advance. To make progress, Black must advance the Pa6. The White K blockades and liquidates Pa6 in exchange for Pb2 (which could be on the c-file after a capture), leaving a book draw. Thus, Black must avoid the Q exchange to have a win, but he can not, as follows.

White has 2 squares c3 and d4, which "support checks" to exchange Qs. Thus, the Black Kc7 must avoid squares on the same row, file, or diagonal as these 2 squares when the White Q has access to them.

<I spent a lot of time trying to force a win after 32...b3 33.axb3 <cxb2> 34.Kxb2 Nxd5

but could not find anything decisive. There are probably a lot of "winning variations", but the double-edged nature of the position makes continual best moves unusually important>

About 3 weeks ago, I had the distinct sense that the puzzle difficulty had flattened through the week, with Monday difficult for beginners and Sunday accessible to CG puzzle regulars. The "new" difficulty is great for me but probably not so good for CG, which should rope in beginners with the usual Monday drill on Q sacs.

At the time I tried to sove the puzzle the game had 38 moves and the final position was reached after 38. Qxc3, draw agreed.

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So this was the "final" position I was taking about (and I think it was the same for <once>).

Here I found that 38. Rg8 wins for Black

39. Ne2 Rg2 40. Qc4 (found no better move) Nxc2 41. Rd1 Nb4 42. Qf7+ Kb8 43. Qf8+ Ka7 44. Qe7 Nb7 45. Qe3 Qb6 and White is lost.>

There’s a spectacular offshoot of the above line developed by <lostinspace> that produces a winning advantage for black.

39...<Re8>

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Now the fireworks begin.

40 Nc1 (unforced) Rxe1 41 Qxe1 Qa1+! 42 Kxa1 Nxc2+! 43 Kb1 Nxe1.

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In my endgame post, because it was directed to you, I edited out as inappropriate a thoughtlessly condescending start: "This might be obvious, but..." Now, everything makes sense: it <would have been> obvious.

<lost in space> is absolutely right. When I looked at the position this morning, the game score ended with 38. Qxc3 1/2 - 1/2. Hence we were both surprised. Why should this position be a draw?

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Now that CG has added in the missing moves to 52. Kb7, is is clearly a draw. Black let slip an advantage that Fritz judged as -4.2 after 38. Qc3 to a level position by move 52. Fritz really does not like 42. ... Rd7, preferring to keep the pieces on with 42. ... Kc6.

<woodywoodpusher> If Black takes the rook, this happens:

32. ... Nxd5 33. Qd4 Nb3 34. Qxh8

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you are absolutely right, 39... Re8! is better than 39...Rg2.

Like your line a lot. Even without 40. Nc1 Black gets a won position, e.g.

38... Rg8 39. Ne2 Re8! 40. Qc4 Re5 41. Qc3 Qa2+ 42. Kc1 Nd5 43. Qc4 Ne3 44. Qf7+ Kb6 45. Qg8 Qe1+ 46. Kd2 Nf1+ 47. Rxf1 Qxf1 and White can resign

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here 2 lines after 32...Nd5:

32...Nxd5 33. Qd4 Nb3!

A: 34. Qxh8 Nd2+ 35. Kc1 Qxa2 36. Qh5+ Kf8 37. Qf5+ Ke7 38. Re1+ Kd8 =

I thought 38 ...Re8 and some following moves had enough force to get something going. Didn't see the game continuation as working at all.

Hmmm-mmm.

Normally, we have an advantage over the players because of the artificiality of the puzzle. We know that there is a tactical shot in the position and so we are on the lookout for forcing moves.

But today's puzzle is different because we are in the middle of a combination - and unusually it is a combination that the opponent has just launched. White has thrown away a piece with 31. Nh8+. So Black would be looking for the thinking behind White's apparent generosity. Why did white give away a knight to lure my rook to h8?

That would lead Black to spot the problems with 32. ... Nxd5 that <lost in space> has well described. This would in turn prompt Black to look for a way to refute the combination. And that is when 32. ... b3 becomes easier to spot. It is a counter-threat which white has to deal with, and which crosses his combination.

When we look at the position cold, with no knowledge of the moves leading up to it, we are at a considerable disadvantage compared to the players.

<1. d4 Nf6 2. Bg5 c5>

This is a variation of the Queen's pawn game known as the Trompowsky (seehttp://en.wikipedia.org/wiki/Trompo...) that has only been occasionally explored at Master level.. More frequently played here by Black are 2...Ne4 as in Miladinovic vs M Vachier Lagrave, 2008; 2...e6 as in Nakamura vs M Al-Modiahki, 2008 and 2...d4 as in V Beim vs Karpov, 2008.

<3. d5>

A slightly more popular
alternative is 3. Bxf6 as in
P Wells vs Shirov, 2006.

<3...g6 4. Nc3 Bg7>

A good alternative is 4...d6 as in A Stefanova vs I Sokolov, 2007.

<5. e4 h6 6. Bd2>

The game appears to enter unexplored territory as this is the first game with this move in the Opening Explorer. An alternative is 6. Bf4, as later played in Ngoc Truongson Nguyen vs I Caspi, 2005

<6...d6 7. h3 O-O 8. Nf3 e6 9. Be2 exd5 10. exd5 Bf5 11. Qc1 g5 12. h4>

An alternative is 12. g4, when White appears to get a small edge after 12...Be4 13. Nxe4 Nxe4 14. h4 Nxd2 15. Qxd2 f5 16. hxg5 fxg4 17. Nh2 g3 18. fxg3 Qxg5 19. Ng4 Nd7 20. O-O-O Nf6 21. Nxf6+ Bxf6 22. Rxh6 Qxd2+ 23. Rxd2 Kg7 24. Rh5 .

<12... g4>

Black has achieved dynamic equality in a complex and difficult position.

<13. Nh2 h5 14. Bh6 Bg6 15. Bxg7 Kxg7 16. Nf1 Nbd7 17. Ng3 Re8 18. Qd2 a6 19. O-O-O b5 20. Bd3 Re5 21. f4 gxf3 22. gxf3 b4 23. Nce2 Qa5 24. Kb1 c4 25. Bxg6 c3 26. Qd4 fxg6 27. Nf4 Nc5 !?>

This worked out OK for Black, but safer and objectively better (especially in light of a strong move Black overlooked on his next turn) IMO is 27... Kh7 =.

<28. Rhg1>

This insures White a small advantage with strong play, but IMo he has a better alternative. Instead, White appears to have a near forced win with 28. Qg1!, when play might continue 28...Rg8 29. Nf5+ Kh7 30. Nxd6 Qc7 31. Nf7 Rf5 32. Ng5+ Kh8 33. d6 Qb7 34. Qd4 cxb2 35. Rhe1 Na4 36. Rd3 Qb6 37. d7 Nc3+ 38. Kxb2 Qa5 39. Kc1 b3 40. axb3 Qa1+ 41. Kd2 Nb1+ 42. Rxb1 Qxd4 43. Rxd4 Nxd7 44. Rxd7 Rxg5 (44... Rxf4 45. Rh7#) 45. hxg5 Rg7 46. Rxg7

<28... Kf7 29. Nxg6 Rxd5 30. Qe3>

White sets a trap for Black, and
prepares a difficult combination that almost back fires on him. A safer alternative, offering white a small advantage, is 30. Qc4 Qb5 31. Qxb5 Rxd1+ 32. Rxd1 axb5 33. Nf4 Re8 34. Ngxh5 Nxh5 35. Nxh5 Re3 36. Rf1 =.

<30... Re8>

Capturing the unprotected Knight leads to mate after 30... Kxg6?? 31. Nxh5+ $1 Kxh5 32. Rg5+ Kh6 33. Rg2+ Kh7 34. Qe7+ Kh6 35. Qxf6+ Kh5 36. Rxd5#.

<31. Nh8+ Rxh8 32. Rxd5 b3!!>

This clever move solves the
difficult Saturday, Aug 16, 2008 puzzle by avoiding a clever trap and initiating a strong counterattack, which in essence amounts to a near decisive positional exchange sacrifice.

Perhaps Black can get away with 32... Nxd5!?, when both sides might have a difficult time in trying to find an equalizing line like 33. Qd4! Nb3

[33... Nf6? 34. Nf5 Ncd7 35. Rg7+ Ke836. Nxd6+ Kd8 (36... Kf8 37. Rf7+ Kg8 38. Qc4 Qc5 39. Rf8+ Kh7 40. Qf7+ Kh6 41. Rxh8+ Nh7 42. Qxh7#) 37. Nb7+ ]

34. Qxh8

[34. cxb3!? Qc5 35. Qxc5 (35. Qxh8?? Qxg1+ 36. Kc2 Qf2+ 37. Kd3 Qe3+ 38. Kc4 Nb6+ 39. Kxb4 Qc5#) 35... dxc5 .]

34...Nd2+ 35. Ka1 Nf6 36. Ne2 cxb2+ 37. Kxb2=.

<33. axb3 Nxd5>

However, Black could have secured strong winning chances with 38...Rg8!, when play might continue 39. Ne2 Rg2 40. Qf6 Nxc2 41. Qe7+ Kc8 42. Qe8+ Kb7 43. Qe7+ Ka8 44. Rd1 Nb4 45. Nc3 Nb7 46. Qe4 Qb6 47. Rc1 Qf2 48. Na4 Qd2 49. Nb6+ Ka7 50. Nc4 Qd3+ 51. Qxd3 Nxd3 52. Rc3 Nbc5 53. Ka2 Rg1! 54. Rxd3 (54.Rc2 Nb4+ 55. Ka3 Nxc2+ 56. Ka2 Ra1#; 54. b4 Nxb4+ 55. Ka3 Ra1+ 56. Kxb4 Ra4#; 54. f4 d5 55. b4 Nxb4+ 56. Ka3 Nbd3 57. Ka2 dxc4 58. Rxc4 Rg4 59. b3 Rxh4 60. b4 Rxf4 -=) 54... Nxd3 .