Puzzle of the week #138

Level: 
4-Rook
Chess Diagram: 

--r---k-
---bpp-p
---p-npQ
----q---
rp-NP-P-
-----PN-
PP-----P
-K-R--R-

Another opposite wing attack from the Olympiad should convince you: if you want a good result, you need to take calculated chances/ risks. Rarely the opponent will roll over nicely and let you win the game. You must take it from him! In order to do that you need to play well in all aspects of the game. Attacking and defending should be done with focus and precision. Here is a small sample of how the position above was played:
21.Ngf5 Nxe4 22.Qe3 gxf5 23.gxf5+ Ng3 24.Rxg3+ Kh8 25.Qg5 Ra5
Your tasks:
a) Explain the move sequence above;
b) White looks again at his defence 26.Qd2 ... What should Black do?

Total available points for this puzzle is 20. The answers will be published next week together with puzzle #139.

Puzzle #137 solution:
Game GM Corrales Jimenez, Fidel  (Cuba) - GM Stellwagen, Daniel (Netherlands), 39th Chess Olympiad 2010 Khanty Mansiysk, Russia. This time we have an excellent solution from Karl.
"a) Analysis:
Material: Black has an extra pawn.
King safety: The Black King is a bit safer. The White King is not defended very well on one side.
Position: pieces of both sides are all developed and all have good mobility: Rooks are on semi-open files, Knights are both active and the Queens can be used easily (well, after a few moves the black queen can).
White has a battery on the e-file, looks menacing with the Knight extended and the pieces pointing towards the White King. Black is defending instead.
Conclusion: White seems to have a better position, but it all comes down to the moves.
Plan for White: Win some material by taking advantage of the e- and f- files, and try to get a attack going.
Plan for Black: counterattack on the Queenside and try to checkmate Black or win some material.
b) Line:
1... Nxc3!
Distracting the defender; if White goes 1... Rxf3, then black wins Nf7.
2.bxc3 Rb8!
Threatening 3... Qb1+ 4.Kd2 Rb2+ winning the Queen for a Rook. Qe2-e4 is the only move for White. If say 3.Qxc4 ... instead, then 3... Qb1+ 4.Kd2 Rb2+ 5.Ke3 Qxe1+ winning the Rook.
3.Qe4 Ba3+
Line (1A) 4.Kd2 Rb2+
If (1B) 4.Kd1 ... then 4... Rb1+ 5.Kd2 ... goes back into (1A)
If (1C) 4.Kc2 ... then 4... Rb2+ transposes into (1A)
5.Kd1 Qxe4
If 5.Kc1?? Re2+! wins easily
If 5.Ke3? Re2+!! (Eugen - this was actually played in the game and White resigned) 6. Rxe2 Bc1+! 7. Rd2 Bxd2+ 8. Kxd2 Qxe4 0-1
6.Rxe4 Reb8 7.Ke1 ...

If white moves anything else instead, then black simple goes Rxa2, followed by Rb1#. If 7. Ke1 Rxa2? then 8. Kf1 and black no longer has checkmate.
7...  Rb1+ 8.Ke2 Rb2+ 9.Ke3 Re1+ 10.Kf4 Rxe4 11.Kxe4 Re2+ 12.Kf4 Kxf7 0-1 or 12. Re3 Rxe3 13. Kxf7 0-1
I discovered this line completely by accident as I was playing around from this position. I’m surprised White lasted that long without getting checkmated."

Correct solutions:
Karl - 20 points
Jeffrey, Alex, Nathaniel - 10 points

STANDINGS

Karl - 210 points
Jeffrey - 197 points
Rick - 174 points
Frank - 122 points
Owen - 95 points
Alex - 81 points
Edwin - 72 points
Nathaniel - 50 points

Comment: 

No second chances