Fischer – Korchnoi1962
Fischer with the Austrian Attack, Korchnoi with the Pirc, at the tournament that decided the challenger for 1963. White's three centre pawns advance, Black hits them with …c5 at once and gets the pawn back with a check, and the middlegame is a brawl Black wins because his queenside is already open. A lesson in not waiting.
Inside your repertoire until move 5