Jul1418
  al wazir: I got 17...Rxf2, expecting the game to go 18. Kxf2 Qxe3+ 19. Ke1 Nxd4 20. Bxd4 Qxd4. Material is even and black's position is strong, if not overwhelming. I never looked at 18. Nxc6. It may be better than taking the ♖. But in the game as played I flat out don't understand 20...Rxe2+. After 21. Kxe2, where's the win? 

Jul1418   diagonalley: the rook sac looks very tempting, but is difficult to calculate with precision... would take courage to play OTB (GMs excepted, of course) 

Jul1418
  wtpy: Al wazir, How about 21..Bg4+ and if 22 Kd2 Nd5+ winning queen; and if 22 Ke1 Ng2 mate? I too overlooked Nc6 as resource for white after Rf2. 

Jul1418   Mayankk: Missed it completely. Too obsessed with making 17... Nxe3 18 fxe3 Qxe3 work. It soon leads to a deadend but I somehow didn’t even think of 17... Rxf2. 

Jul1418
  jith1207: Rxe2 opens up diagonals for Black's bishop in both sides, Bg4 and Ba4. If white takes by Nxe2, Ng2+ forces white king to move too d1, where Ba4+ would claim the white queen for free after Qc2 Ne3+. White loses queen or more material, if not getting mated, in more ways than one. I saw Rxf2 instantly, but could not string together any continuation. Analyzing the game shows how overwhelming the position actually is. 

Jul1418   NBZ: I saw Rxf2 Nxc6 Nxe3, but did not have a clear idea of how to proceed once White moved his queen: the thought of Rhf8 came to my mind, but I have to admit I did not see how strong Black's attack would be. Would I have gone for the piece sacrifice had I been playing the game? I am not sure. 

Jul1418
  An Englishman: Good Evening: Saw 17...Rxf2; 18.Kxf2,Qxe3+; 19.Ke1,Nxd4. Black has a very strong position, but no forced win. Looked like one of those puzzles where you can't see everything and you have to rely upon your intuition. But White played 18.Nxc6, which led to immediate defeat, and I move I dismissed without much consideration. What do you thinkdo I dock myself a half point for ignoring a mistake? 

Jul1418   Jamboree: After 19. ... Ref8, why doesn't white just make the obvious move, 20. Qxg7+, saccing the bishop back in order to get the dangerous black queen off the board, neutralizing black's threats? I see 19. ... Ref8
20. Qxg7+ Qxg7
21. Bxg7+ Kxg7
22. Nd4
...which rescues the knight and simultaneously prevents black's threatened Nc2 fork. Yes, in the resulting position black is a pawn up with a slightly better position, but I see no immediate win, as the white knight at d4 is pretty strong and hard to dislodge. Sure, black may win anyway in the long run, but not in some immediate queenwinning/mating crush as in the game line, but instead after a long hardfought endgame. This being the case, is the "winning" solution line really as devastating as we have been led to believe? 

Jul1418   Imran Iskandar: My first thought was Nxe3, but then saw that Rxf2 might be more promising. I was thinking on the lines of 17...Rxf2 18. Kxf2 Rf8+ 19. Ke1 Qxe3 but wasn't too sure what would happen next. I saw 20. Rf1 Rxf1+ 21. Kxf1 Bh3+ 22. Ke1 Qg1+ 23. Kd2 e3+ 24. Kd3 Ne5+ 25. Ke4 where White just looks doomed. As for the possibility of refusing the rook sacrifice, I just assumed that if 18. Nxc6 then simply bxc6 and the attack somehow continues. The game continuation from move 18 to the end didn't really enter my head. 

Jul1418   Imran Iskandar: Hmm, turns out that 18...Rf8+ in my analysis is very bad and Qxe3+ was the way to continue the attack. 

Jul1418
  gofer: <17 ... Rxf2>
I don't think white can accept the sacrifice as black has the following
combination <18 Kxf2 Qxe3+ 19 Ke1 Nxd4 20 Bxd4 Qxd4>, which at the very
least gains two pawns for going an exchange down, but as Ra1 is loose
it gain a tempo and black can start the two central connected passed pawns
rolling (after 21 Rd1 Qc3+ 22 Qxc3 Nxc3 23 Rd2 Nxe2)... 18 OOO Qxe3 +
18 Nxc6 Nxe3 +
~~~
I didn't see the full threats of <18 ... Nxe3>, but I was close for only a
few minutes work! So perhaps this is too easy for a Saturday... <18 ... Nxe3>
<19 Qc3 Ref8>
<20 Nd4 Rxe2+> 21 Nxe2 Ng2+
23 Kd1 Ba4+!!!
21 Kxe2 Bg4+
22 Nf3 Bxf3+ (Ke1 Ng2# or Kd2 Nd5+ +)
23 Ke1/Kf2 Bxh1/Kxh1+ + 

Jul1418   Walter Glattke: A) 17.Rxf2 18.Kxf2 Qxe3+ 19.Kg2!? Nf4+
20.gxf4 Bh3# / 20.Kf1 Nd3 21.Bxd3 Bh3#
19.Kf1 Nf4  so 19.Ke1 Ne5! better than Nd4 20.Qd2!? Nd3+ 21.Kd1 Ba4+  so 18.Nxc6 is good thought, denies 18.Kxf2 Qxe3+ 19.Ke1 Ne5!
B) 20.Rxe2+ end position in the match: 21.Kxe2 Bg4+ 22.Ke1 Ng2# 22.Kd2 e.g. Nd5+23.Qe3 Qxe3+ but 21.Nxe2 Ng2+ 22.Kd1 Ba4+ 23.Qc2 Ne3+! 

Jul1418
  gofer: Another combination I missed (in the line where white accepts the
rook sacrifice).
18 Kxf2+ Qxe3+
19 Ke1 Nxd4
20 Bxd4 Qxd4
21 Rd1? Ne3!!!
22 Qc1/Qb1/Qd2 (Rxd4 Nxc2+ +) Ng2+ mating!!!!
So the rook can't go to d1.
21 Qd1 Qc3+
22 Kf2 Rf8+ (Kf1 Ne3+ +)
23 Kg2 Qe3!
24 Qe1/Qg1 Nf4+!
25 Kf1/gxf4 Bh3#!!!
So the queen can't go to d1.
22 Rc1 Ne3
23 Qd2 Ng2+ (Qc3 Ng2+ 24 Kf1 Rf8+ +)
24 Kd1 Ba4+
So the rook can't go to c1.
Hmmm, so it looks like white was absolutely right not
to accept the rook sacrifice. White's defences are in
tatters after Qxe3+ and Nxd4 

Jul1418
  ChessHigherCat: 19. Kf1 leads to this nightmarish position, where white has a choice between a various royal forks and Qxa8: 18. Kxf2 Qxe3+ 19. Kf1 Nxd4 20. Bxd4 Qxd4
click for larger view21. Rd1 Ne3+ 22. Kg1 Nxd1+ 23. Kg2 Qf2# 

Jul1418
  patzer2: Since it was a difficult Saturday puzzle, I guessed the first move was the demolition 17...Rxf2!!. I also guessed the Black response would be 18. Nxc6, but I was pretty much clueless as to how to followup. My planned response 18...Qxe3 fizzles out to a near level position after 18...Qxe3 19. Bd4! (all others lose) 19...Qxe2+ 20. Qxe2 Rxe2+ 21. Kxe2 Bxc6 22. Bxa7+ Bb5+ = to ⩱ (0.22 @ 35 ply, Stockfish 8). Instead, the game move 18...Nxe3! + (6.70 @ 30 ply, Stockfish 8) or the second best option 18...Ref8! + (6.25 @ 30 ply, Stockfish 8) both give Black a winning attack. P.S.: White's decisive mistake was 17. g3?, allowing today's Saturday puzzle solution 17...Rxf2!! + (6.70 @ 30 ply, Stockfish 8). Instead, Black can hold it level with 17.Nxc6 bxc6 18. Qd2 = (0.00 @ 31 ply, Stockfish 8). 

Jul1418
  thegoodanarchist: My old engine, Deep Shredder 12, found 17...Rxf2 instantly, as soon as I made the move 17.g3. It gives the following lines:
17... Rxf2 18.Nxc6
(18.Kxf2 Qxe3+ 19.Ke1 Nxd4 20.Bxd4 Qxd4 21.Ra2 Rf8 22.Rf1 Rxf1+ 23.Bxf1
Qe3+ 24.Qe2 Qc1+ 25.Kf2 Nc3 26.Qc4 Nxa2)
(18.Qd2 Ref8 19.OOO Bg4)
18. ... Ref8 19.OOO Qxe3+ 20.Qd2 * 

Jul1418
  agb2002: Black has a bishop and a knight for the bishop pair. Several squares around the white king are weak. This leads to 17... Rxf2: A) 18.Kxf2 Qxe3+
A.1) 19.Ke1 Nxd4 20.Bxd4 (20.Qd2 Nf3+ wins) 20... Qxd4 A.1.a) 21.Rd1 Ne3 22.Qd2 (22.Rxd4 Nxc2+ 23.Kd2 Nxd4  + [n+2p]) 22... Ng2+ 23.Kf1 Rf8+ 24.Bf3 (24.Kxg2 Qf2#) 24... Ne3+ 25.Ke2 Qxd2+ 26.Rxd2 Rxf3  + [n+2p]. A.1.b) 21.Rc1 Ne3
A.1.b.i) 22.Qa2 Ng2+ 23.Kf1 Rf8+ 24.Bf3 Bb5+ 25.Kxg2 exf3+ 26.Kh3 Bd7+ 27.g4 Qxg4#. A.1.b.ii) 22.Qc3 Ng2+ as above.
A.1.b.iii) 22.Qd2 Ng2+ 23.Kd1 (23.Kf1 Qxd2 wins) 23... Ba4+ 24.Rc2 Ne3+ 25.Ke1 (25.Kc1 Qa1#) 25... Nxc2+ wins decisive materal. A.1.c) 21.Rb1 Ne3 looks similar to A.1.b. Black has Rc8+ if the White king moves to c1 eventually. A.2) 19.Kf1 Nxd4 20.Bxd4 Qxd4 as above. For example, 21.Rd1 Rf8+ (or 21... Ne3+) 22.Ke1 Ne3, with the double threat Ng2# and Nxc2#, wins. A.3) 19.Kg2 Nxd4 20.Bxd4 (due to Nxe2 and Nxc2) 20... Qxd4 seems to win. For example, 21.Qa2 (due to Ne3+ and to protect the rook on a1) 21... Ne3+ 22.Kf2 (22.Kg1 Nd1+ 23.Kf1(g2) Qf2#) 22... Rf8+ 23.Ke1 Qc3+ 24.Qd2 Qxa1+ wins. B) 18.Nxc6 Nxe3 (18... Qxe3 19.Bd4 Rxe2+ 20.Qxe2 Qxe2+ 21.Kxe2 Bg4+ 22.Kd2 bxc6 23.Bxa7 looks better for White) B.1) 19.Qd2 Ng2+ 20.Kd1 (20.Kxf2 Qxd2 wins decisive material) 20... e3 followed by Bxc6 with the threats Bf3 or Ba4 looks good for Black even with the momentarily trapped knight. B.2) 19.Qc3 Rxe2+ 20.Kxe2 Bg4+
B.2.a) 21.Kd2 Nd5+ wins decisive material.
B.2.b) 21.Ke1 bxc6 and Black has two pawns for the exchange and keeps the attack. For example, 22.Qxc6 Rc8 23.Qxe4 Nc2+ 24.Kf1 Nxa1 25.Bxa1 Rc1+ 26.Kf(g)2 Qd2+ 27.Qe2 Qxe2#. B.2.c) 21.Kf2 Rf8+ 22.Kg1 (22.Ke1 Ng2#) 22... bxc6 as above. B.3) 19.Qc1 Rxe2+ looks similar to B.2. 

Jul1418   nisharaj31: What is the winning line after 21Nxe2? 

Jul1418
  malt: <nisharaj31:> 21...Ng2+ 22.Kd1 Ba4+ 23.Qc2 Ne3+ 

Jul1418   MrCarciofo: Either after Kxe2 or Nxe2 White loses its Q and the game: if Kxe2: ...Bg4+; Kd2, Nd5+ (if Ke1, Ng6+; Kd1, Ba4+ and White loses its Q and then mate); if Nxe2, Ng6+; Kd1, Ba4 and White loses its Q and mate). 

Jul1418
  Richard Taylor: I saw Rxf2 but not White's reply. I also wondered about Nxe3 also. Rxf2 was my initial idea but I couldn't see all the moves. I think it was more a positional sacrifice Black played breaking open White's position. At the end Black is relying on a superior activity of his pieces but White may have had more play. 

Jul1418
  Richard Taylor: At the end:
20...Rxe2+
21. Kxe2 Bg4+ 22. Ke1 Ng2#
or 21. Kxe2 Bg4+ 22. Kd2 Nd5+ 23. Kc2 Rf2+ 24. Kb3 Nxc3 25. Bxc3 Qe3 26. Rae1 Qd3 27. h3 Be6+ 28. Nxe6 Qc2+ 29. Kc4 Rf3 30. Rc1 Rxc3+ 31. Kd4 Qd2+ 32. Kxe4 Re3+ 33. Kf5 Qd5+ 34. Kg4 Qxe6+ 35. Kh4 g5+ 36. Kxg5 Re5+ 37. Kh4 Qh6+ 38. Kg4 Qh5+ 39. Kf4 Qf5# None of it forced just me playing around but it is a possible line. Black has to watch out for back rank mate and the White Q and B delivering mate on g7.... If 21. Nx2 then
21. Nxe2 Ng2+ 22. Kd1 Ba4+ looks pretty winning. 

Jul1418   bebgsurg: What about 20. Ne7 for white, then 20.....Kg8 and 21. Ng6 QxN then 22. QxN on e3 equalizing or white better? 

Jul1418
  ChessHigherCat: <bebgsurg> 20) Ne7 Kg8 is impossible because the king can't move into check 
