[Event "URS-ch sf"]
[Site "Gorky URS"]
[Date "1950.??.??"]
[EventDate "?"]
[Round "12"]
[Result "1-0"]
[White "Tigran Vartanovich Petrosian"]
[Black "Anatoli Sidorov"]
[ECO "D43"]
[WhiteElo "?"]
[BlackElo "?"]
[PlyCount "83"]

1. Nf3 {Notes by Peter Clarke} Nf6 2. d4 d5 3. c4 e6 4. Nc3 c6
{Up to here neither player had revealed his hand much. But now
Black, by his adopting his initial position of the Semi-Slav,
seems to be showing agressive intentions,. He is unwilling tio
meet the hazards of meeting a prepared variation in the Meran
(5.e3 Nbd7 6.Bd3 dxc4 7.Bxc4 b5) or the even sharper
Anti-Meran (5.Bg5). He wants to keep the play on a line of his
own choosing.} 5. cxd5 exd5 {Sidorov is determined to have a
keen struggle. The alternative Exchange Variation (of the
slav), which he could have had by recapturing with the other
pawn, is considered to give Black a comfortable, if dull,
game.} 6. Qc2 Bd6 {The Bishop is better placed on e7, where it
can counter White's Bg5. The point is that before undertaking
anything else Black should think in terms of equalising.}
7. Bg5 O-O 8. e3 Nbd7 9. Bd3 Qc7 {This would not have been
necessary had his sixth move been correct. Black has now the
same battery of Queen and Bishop as White, but in
effectiveness there is no comparison-especially after White's
reply.} 10. O-O-O {! Indeed, Black's pieces are, as it were,
facing the wrong direction. Normally, the so-called minority
attack is the first choice, while castling Q side and
advancing on the other wing, being rather double-edged, is
less frequently seen. In this case it is clearly the right
strategy, for Black is ill-prepared for making a
counter-attack.} Re8 11. g4 {There is to be no
time-wasting. Already Black is faced with the threat of
12.Bxf6 Nxf6 13.g5. Since both 11...Nxg4 and 11...h6 would
only accelerate trouble, he decides to give up a pawn and try
to use the respite to start his own plans moving. It is the
best practical chance.} Kh8 12. Rdg1 b5 13. Bxf6 Nxf6 14. g5
Ne4 {!} 15. Nxe4 dxe4 16. Bxe4 Be6 {The sacrifice has resulted
in an opening of lines in the center and on the Q side and,
consequently, in the increased activity of the Black
pieces. His Bishops, in particular, have suddenly become
hostile and could easily take the lead in a dangerous attack
on the King. At the same time, White finds that his attach has
slowed down, and despite the promising beggining six moves ago
he still lacks an open file on the K side. How, then, can be
put new life into this game and get the initiative back?
Petrosian provides an energetic answer.} 17. g6 {! The main
point is the clearance of the g5 square for the Knight, an
idea which cannot be foiled by 17...f6 because of 18.gxh7
followed by N-h4-g6+} hxg6 18. Ng5 f5 {Otherwise (for
instance, 18...Bxa2) White smahes his way through by
19.Bxg6. The same would have applied if the f-pawn had made
the capture on the previous move.} 19. Nxe6 Rxe6 20. Bf3 {! He
could still win a pawn by 20.Bxc6, but that would be entirely
contrary to the theme of the game and, moreover, give his
opponent renewed hopes of counter-play after 20...Rc8 21.d5
Re4.} Rc8 21. h4 c5 22. d5 {Spelling the end for Black; he can
now do nothing to stop the storm breaking on the K side.} Rf6
23. h5 g5 {Or 23...gxh5 24.Rxh5+ Kg8 25.Rxf5, etc.} 24. Rxg5
c4 25. Kb1 {But not 25.Rxf5? c3! when the pawn cannot be
by-passed by 26.b3 on account of 26...Ba3+} Rcf8 26. Rhg1 R8f7
27. Rg6 Be5 28. h6 gxh6 29. Rg8+ Kh7 30. Bh5 Rf8 {An exchange
of Rooks is forced now, since if 30...Re7, then 31.f4 Bd6
32.Qg2 is crushing (33.Rh8+ is the threat)} 31. Rxf8 Rxf8
32. f4 Bg7 33. Bg6+ Kh8 34. Bxf5 {Three connected passed pawns
in the center represent a tidy profit-and the assault is not
finished yet.} Qc5 {34...Qd6 35.Qg2 Qf6 36.e4 was just as
bad.} 35. Qg2 Qe7 36. Qg6 {In a way this would have been a
fitting moment for Black to resign. Kis g6 has proved a fatal
square for him, and now White's most powerful piece has
settled on it. Sidorov reckons he ought to fight on a little
longer.} Rxf5 37. Qxf5 Qxe3 38. Rd1 Qf2 {If 38...c3, White
ignores it. The d-pawn wins for him.} 39. Qc2 Qxf4 40. d6 Qf8
41. d7 Qd8 42. Qg6 {!} 1-0