Robert Huebner vs. Tigran Petrosian

Biel - 1976

It's often said of Petrosian that if given the choice between defending against his opponent's mate in three or executing his own mate in 4, he'd choose the former. But in this game from the 1976 Interzonal, Huebner does exactly that.

On White's 37th move, Huebner plays 37. g3, overlooking a forced mate in 4. Next move he sees it, but by then it's gone. The game had enormous implications, since by losing it, Huebner missed out on the Candidates by half a point.