Petrosian takes out Fischer in 1971 and ends his run of 19 consecutive victories:
Of course, Fischer went on to win their Candidate's Final match, in which this game occurred (6.5 - 2.5), and went on to become World Champion the following year. Coming into this match, Fischer had beaten Taimanov 6-0 in the quarter-final round, then Larsen 6-0 in the semi-final, while Petrosian had defeated Hubner 4-3, then Korchnoi 5.5-4.5.
Petrosian is one of my very favourite players - a true master of subtlety. This is game 55 from 'Petrosian vs the Elite: 71 Victories by the Master of Manouevre 1946-1983'.
It's still a good idea to castle most of the time, even if your name is Bobby Fischer.