This game, like almost every other one in this historic match is just the opposite of the stereotypical "GM Draw" and is possibly not only the greatest struggle in this WCH but also one of the greatest games ever played in a WCH. Going into the game with a one pt deficit after only three games Fischer now needed to score 11.5 pts in the remaining 21 games while Boris only needed to score 10 pts in order to draw the match and retain his crown; yet Bobby courageously played his trusty Sozin Attack even though he must have known Spassky and his second GM Geller (+5 - 3 vs FIscher) would have something "up their sleeves" for his pet line, with which he lost to Geller in just 24 moves in 1967 - and is one of three losses included in his monumental "My 60 Memorable Games."
Today the Sozin Attack is now known as the Fischer Variation in honor of his pioneering efforts beginning in the late 1950s to ressurect a once obscure line overshadowed by the Najdorf, Dragon, Schveningen and Richter-Rauzer Variations and making it just as popular and respectable as any other main line in the Sicilian Defense.
I suggest downloading the pgn file here and going over this game with extensive annotations by several world-class GMs in your own chess program or database, where you can see a full page of the game moves, alternate moves and commentary at a time.
Halldor Petursson was a famous Icelandic caricature artist who drew 18 cartoons of the match for a local newspaper. You can see them all at http://www.dos.is/chess/3_halldor_postcards.html
In this one Cowboy Bobby attempts to "rustle" Spassky's crown with a lasso while Chief Arbiter GM Schmid (wearing glasses) and the assistant arbiter calmly observe the action.