21 h2+

Option 1 (which white probably avoids as it loses an exchange and ends in roughly the same position, but 2 moves later):

21 ... Kg7
22 Bh3+ Kxh2
23 Bxf1 Rxf1
24 Qe6

Option 2 (when white can probably wriggle out of mate but at what cost?)

21 ... Kxh2
22 Qe6

Now white needs to create an escape sqaure for his king otherwise we get the following combination (22 ... Nf4 23 Ng4+ Kg1/Kg2 24 Qh6 with Qh2+ following)

22 ... Rfe1/Rfd1
23 Qh3+ Kg1
24 Ng4 Bg7
25 Nf3+ Bxf3 (Kf1 26 Nh2#)
26 Qh2+ Kf1
27 Qxf2#

22 ... f4
23 Qh3+ Kg1
24 Ng4 Rf2
25 Nf3+ Bxf3
26 exf3 Rxf3 (Nd4 Bxd4 exd4 opening the e-file game over) 27 Qh2+ Kf1
28 Nde3+ Ke1 (Rxe3 29 Rxe3 and its game over after Bxc3) 29 Qh1+ winning

22 ... f3
23 Qh3+ Kg1
24 Nxf3+

24 ... Rxf3 (losing the exchange)
25 exf3 Bxf3
26 Rxe3 opening up the e file which is winning...

24 ... Bxf3
25 exf3 Rxf3
26 Ng4

with the following coming again as above, I dont think white has many options...

27 Qh2+ Kf1
28 Nde3+ Ke1 (Rxe3 29 Rxe3 and its game over after Bxc3) 29 Qh1+ winning

J Ragan vs Benko, 1974 (21...?)

Black to play and win.

Material: Even. The White Kg1 has 1 legal move, h7, and is vulnerable to 21…Nf3+ or 21…h2+. The White K-side is lightly defended, and Bd7, Nf6, and Ng5 are ready to exploit its weak light squares. In particular, the Black Ph3 blocks h3, suggesting a clearance, and moreover, the indefensible squares h2 and h3 beckon the Black Qe7. The Black Kg8 is secured from check.

Candidates (21...): h2+

21…h2+

(1) 22.Kxh2 <Nf3+> (threatening 23…Nd2 forking Qb3 and Rf1)

[Toga evaluates 22...Nf3+ at about -3 P for White vs. 22...Ng4+ at about -16 P.]

23.Bxf3 exf3

(1.1) 24.Ng1 Ng4+ 25.Kh3 Nxe3+ 26.Kh2

26…Qe6 (threatening 27…Qh6+ 28.Nh3 Qxh3#)

27.Nxf3 [or Ne2] [g4 Qe5+ 28.Kh3 Bxg4+ 29.Kh4 Bf6#]

27…Qh3+ 28.Kg1 Qg2#

(1.2) 24.Nf4 Ng5+

25.Kg1 [Kh3 Nxe3++ then 26…Nxf1 is enough to win]

25…Qf6 (threatening 26.Qh6 27.Qh2#)

Black has no feasible defense.

(2) 22.Kg2 Bh3+ 23.Kxh2 Bxf1 is enough to win

White's play is predicated on the idea that his king is safe, and that the center is stable. He effectively ends his game with 11. Rc1? missing his chance to prevent Black's e4.

There seems to me to be two main lines, depending on whether White captures the pawn or moves ♔g2. I believe the latter, rather than the game move, is best for White. I would continue playing:

22. ♔g2 ♗h3+ 23. ♔xh2 ♗xf1 24. ♘f4

(25. ♖xf1? leads to a devastating attack by Black starting with ... ♘g4+! and followed by ... ♕f6)

... ♘g4+ 25. ♔g1 ♗d3 26. bxc6

(♘xd3 ♘h3+ 27. ♔g2 ♙exd3 28. ♔xh3 ♘xf2+ 29. ♔g2 ♕xe3)

...♕e5 27. ♘b5 ♗f8 (allowing the queen to be brought to the h-file)

28. ♕d1 ♙f5 29. ♗g2 ♕h8 30. ♘xd3 ♕h2+ 31. ♔f1 ♘h3 32. ♗xh3 ♕xh3+ 33. ♔e1 ♕g2 34. ♖c2 ♙exd3 35. ♕xd3 ♕g1+ 36. ♕f1 ♖xe3+! 37. ♙fxe3 ♕xf1+ 38. ♔xf1 ♘xe3+

click for larger view

When Black picks up the rook on the next move, White's position will be hopeless.

Black to play (21...?) "Very Difficult"

Wow, two games in a row where I was familiar with the games. I just happened to see this on CG when I was going through a lot of games, including some of Benko's.

I remember it went 21...h2+! 22. Kxh2 Ng4+ 23. Kg1 Qf6 and then White had to give up material to stop the mate.

Silman thinking technique:

Material: Dead even.

Minor Pieces: Black’s dark squared bishop is inactive at the moment but when the f6 knight moves, that changes. Black’s light-squared bishop is busy protecting two pawns including the advanced fellow on h3. Black’s g5 knight can jump into the hole on f3 and enjoy the support of the well-protected e4 pawn. The f6 knight can jump to g4 though it’s not clear what this will immediately accomplish. White’s minor pieces are comparatively inactive.

Space: Black enjoys a space advantage on the kingside while white has more space on the queenside.

Pawn Structure: Black has an isolated passer on h3. As mentioned, the e4 pawn provides an advanced home for a knight on either f3 or d3. Black has an isolated pawn on a7. White has two pawn islands, neither of which appear to be doing much. White’s f-pawn is backward.

Key Files/Squares: Besides the nice holes for the knights, the ‘d’ and ‘h’ files are half-open. Black’s light-squared bishop controls the c8-h3 diagonal.

Development: Black’s pieces are more developed. The white king has only one safe square to move to at the moment.

Initiative: I’m embarrassed to say I can’t spot this unless there’s a major threat so let’s move on.

Hmmm. Space advantage on the kingside, active minor pieces on the kingside, advanced h3 pawn and white’s king is exposed… let’s play on the kingside! Candidate moves:
1. Nf3+
2. Ng4
3. Bb4
I’m almost out of time (I give myself three minutes per star) so I’m going with Ng4. It frees up the dark-squared bishop and threatens h2+.

Times up.
---

Crap. If I were to take a guess, I'd say I didn't call nearly enough attention to the exposed king which should have called for an immediate tactic (sacrificing the pawn) followed by the knight check. I got too caught up in other things.

Material is even, but the proximity of the h3-pawn, the immobility of white's Bh1, and the offside location of the white queen indicate strong attacking prospects for black. In general, the key factor for success in such attacks is to create efficient ways for the attacking queen to infiltrate. Therefore, I like

21... h2+

This is forcing; it makes h3 available to black attacking pieces, it prevents this pawn from shielding the h-file, and it gains tempo for bringing the Nf6 into the attack. Now

A) 22.Kxh2 Qe6!

A versatile move, because it threatens direct entry with Qh3+, and is also directed against f3 or f4 defenses.

23.Nf4 Ng4+ 24.Kg1 Qh6 25.Rfe1 Qh2+ 26.Kf1 Qxf2#

A.1) 23.Bg2 Ng4+ 24.Kg1 Qh6 25.Rfd1 Nf3+! 26.Bxf3 (26.Kf1 Ng4h2#) Bxf3 27.Qh2+ Kf1 28.Qxf2#

A.1.1) 24.Kg2 Qh6 25.Rfe1/d1 Qh2+ 26.Kf1 Qxf2#

B) 22.Kg2 Bh3+ 23.Kxh2 Bxf1 24.Rxf1 Qe6 looks like A, with white already an exchange down.

lol

click for larger view

Stockfish_20032521_x64_modern: