This is a somewhat interesting game. Petrosian's only loss in the 1976 Interzonal, and one of only three Interzonal losses that he suffered ever. As upsets go, it's at least as big as Bronstein's loss to Cardoso in 1958, though without the ill effects this time. Petrosian qualified anyway.
Apart from the upset, the game is interesting for the fierce Kingside attack that Castro builds up in a seemingly lost position, for the draw offers, and the missed repetition, but most importantly for what happened after the game.
After winning the game, Castro received a congratulatory telegram from Petrosian's worst enemy, Viktor Korchnoi, accompanied by one hundred dollars in cash, and the message "I pay for my pleasure."
As people were wondering how one Soviet player could so flagrantly disrespect another, given the rather... uh, dim view their government took of such things, Korchnoi defected 2 days later. I guess that's how.