DWINS: Spassky finally got a favorable position against the French Defense for the first time in the match, but messed it up (missing a mate), and then managed to win when Korchnoi overstepped the time limit.
Korchnoi ripped off a center pawn with 14...Nxe5, relying on 15.gxf5 Nxd3 16.cxd3 Qc3 17.Ra2 exf5 to yield him an overwhelming counterattack. Another point of his ingenious piece sacrifice was that 15.Bf4? Nxd3 16.Bxc7 Nxf2+ 17.Ke2 Nxh3 18.gxf5 Rxf5 would have put Black three pawns ahead.
Spassky gave up a second pawn with 19.g5, preparing to punish its acceptance by 19...hxg5 20.Rg1 Rf7 21.Rxg5+ Kh8 22.Qg4 Rg7 23.Qd4! which Stockfish 5 evaluates as (1.48).
Korchnoi prevented the opening of lines against his king with 19...e5
20.Qg3 h5, paying the one-pawn price to 21.Rxe5.
Note that Korchnoi could not play 22...Rf3?? because of 23.Re8+, winning the queen. His alternative, 22...Qg7? was a mistake however. Stockfish 5 gives 22...Rac8 23.Rb3 Qg7 24.Qe3 Rxf2 25.Rxb7 Rfxc2+ 26.Bxc2 Qxb7 27.Re8+ Kf7 28.Rxc8 Bxc8 which only gives Spassky a small advantage (0.57).
One mistake led to another and instead of playing 23...Rxf2 (1.23), Korchnoi's 23...Rf3? should have been followed by 24.Re7 Rf7 25.Rbxb7 (2.87).
Note that in the game continuation, 24...Rd8, 25.Be4 Rxf2! 26.Bxd5+ Kh8 27.Rxb7? fails against 27...Rf1+!
Spassky blundered badly with 27.h3?? giving Korchnoi a winning position after 27...Rf1+, instead of playing 27.Bxd5+ Kh8 28.Re7 Qxd4 29.Rxd4 which Stockfish 5 evaluates as (0.91).
Korchnoi returned the favor by allowing Spassky to equalize after 28...Bxh3?, instead of playing 28...Rd1 29.Bd3 Bxh3 (-1.23).
The ping pong game of errors continued with Spassky missing a chance to equalize with 30.Re7 Qxd4+ 31.Rxd4 Rff8 32.Rxa7 Bg2 33.c4 Bxd5 34.cxd5 Rd6 and Korchnoi failing to maintain his advantage by 34...b5 35.Rxf8+ Rxf8 36.Rxb5 Qxc3+ 37.Kxc3 h4 (-0.82).
Korchnoi could have maintained equality with 36...Rce7 37.Rd8 Rxd8 38.Qxd8+ Re8, but instead cracked with the horrendous 36...h4??? most likely due to time pressure. Spassky, who must have been in terrible time pressure also, missed the killing 37.Rd8!! Re7 38.Rf8+ Rxf8 39.Rxf8#
No other defense would have held up either, for example: 37...Rc8 38.Rd7! Rxc4 39.Rf8+ Rxf8 40.Qxg7# or 37...h6 38.Rxe8+ Bxe8 39.Rxh6#
Instead Spassky's 37.Bb3??? should have allowed Korchnoi to equalize with 37...Rce7, but Korchnoi's 37...h3??? gave Spassky another chance to mate with 38.Rd8. Not only did he miss that, but his 38.Qh4?? should have given Korchnoi a possibly winning game after 38...Bf7 39.Rd2 Bxb3 40.Kxb3 Rec8 41.Qxh3 Qxg5. However, his flag fell before he was able to make his 38th move.
Clearly, extreme time pressure was to blame for the sloppy play in this game, but it's an enjoyable game to play through nonetheless.