Petrosian was world champion at the time. 3 years earlier Fischer played Petrosian in the "Four Queens" game. He had the defensive player of the century playing a game with 4 queens on the board at the same time - rather than take an easy draw. It ended in a draw anyway. http://www.chessgames.com/perl/chessgame?gid=1106430
You Bobby Fischer fanboys are to chess what the Ronaldinho fanboys are to soccer. Yes, Bobby was brilliant, but he was not invulnerable. Matter of fact, Bobby lost some ridiculous games too. See this: http://www.chessgames.com/perl/chessgame?gid=1800759