Force is one of the basic principles of chess strategy. It refers to the strength of the pieces. Having a greater force than your opponent can either mean more pieces overall or more pieces in a particular area of the board. In this game, Fischer applies overwhelming force on the Kingside, resulting in a sensational Queen sacrifice that he had planned several moves in advance.
Fischer-IM Lhamsuren Miagmasuren
Sousse Interzonal 1967
1.e4 e6 2.d3 d5 3.Nd2 Nf6 4.g3 c5 5. Bg2 Nc6 6.Ngf3 Be7 7.O-O O-O 8.e5!
Fischer-The key strategical thrust. My plan is first to drive his defensively well-placed Knight to an inferior square, then slowly ring his cramped King's position with my pieces to mate him. Of course, Black gets counterplay on the opposite wing. The question is: Who comes first?
8...Nd7 9.Re1 b5 10.Nf1 b4 11.h4 a5 12.Bf4 a4 13.a3
Fischer-Believe it or not, I actually spent more time on this innocuous push (15 minutes) than on any other move in the game! I didn't want to allow Black to get in ...a3, which would practically force me to reply with b3, thereby creating holes (weak squares) on c3 and d4. On the other hand, by stopping to meet his positional threat, I am forced to postpone my own schemes for at least one move. Chess is a matter of delicate judgement, knowing when to punch and how to duck.
13...bxa3 14.bxa3 Na5
Placing the Knight on the rim is dubious. Better is 15...Ba6.
15.Ne3 Ba6 16.Bh3
Preventing Black from playing ...f6 or ...f5.
16...d4
Gaining the d5-square, but giving up the e4-square, which will later play a decisive role in White's attack.
17.Nf1
This Knight retreats temporarily, but will later maneuver to the hole at e4.
17...Nb6 18.Ng5 Nd5?
Better is 18...h6 19.Ne4 c4.
19.Bd2 Bxg5
Now 19...h6 is impossible due to 20.Nxe6 fxe6 21.Bxe6+ Kh8 22.Bxa5 Qxa5 23.Bxd5. Black's best try is 19...c4.
20.Bxg5 Qd7 21.Qh5 Rfc8 22.Nd2
More pieces are coming to the Kingside for the decisive attack.
22...Nc3
22...c4 was still the best move.
23.Bf6!
Threatening 24.Qg5 g6 25.Qh6. The Bishop is immune because of 23... gxf6 24.exf6 Kh8 25.Nf3 Nd5 (25...Rg8 26.Ne5) 26.Ng5 Nxf6 27.Qh6 Qe7 28.Bf5 Rg8 29.Nxh7, winning.
23...Qe8 24.Ne4
White will exchange the Knight on c3 in order to bring the Rook to the Kingside via e4. 25.Nd6 is threatened.
24...g6 25.Qg5 Nxe4 26.Rxe4 c4
Black's queenside counterplay is too slow.
27.h5 cxd3 28.Rh4! Ra7
If 28...dxc2, then 29.hxg6 fxg6 30. Rxh7 c1=Q+ 31.Rxc1 Rxc1+ 32. Qxc1 Kxh7 33.Qc7+, mating, or 30... Kxh7 31.Qh4+ Kg8 32.Qh8+ Kf7 33.Qg7 mate. The text move counters this threat by guarding h7. According to Fischer, 28...Rc7 would have been better, although White would still be winning.
29.Bg2!
The Bishop enters the attack by repositioning on the e4-square.
29...dxc2
Fischer-Black started to get excited, thinking I had miscalculated by allowing him this dangerous passed pawn. But he has no better defense. On 29...Bb7 30.hxg6 fxg6, 31.Rxh7! as in the previous note. The point is: Had Black played 28...Rc7 (instead of ...Ra7), this line would not have worked, because 31.Rxh7 would have been met simply by ...Rxh7. White's best, therefore, would have been 30.cxd3 followed by an eventual doubling of Rooks on the h-file, with a finish similar to the actual game.
30.Qh6 Qf8 31.Qxh7+! 1-0
A spectacular finish! If 31...Kxh7, then 32.hxg6+ Kxg6 33.Be4 mate or 32...Kg8 33.Rh8 mate.