Jamboree: After struggling - and not always succeeding -- to maintain equality for 44 frustrating moves, DeFirmian finally broke Karpov's grip with 44. ... Rc8!
The white rook is pinned, so it can't come to the defense of the c4 pawn, which therefore looks doomed. Furthermore, after capturing on c4 with the Q, black will control the checking diagonal, his own a-pawn, and the rook, and so forth, and may even have a winning position.
Luckily for Karpov, however, he may have a saving tactic with 45. d6!?, since both hanging white pawns are momentarily untouchable, due to sneaky follow-up traps with either d7 or c5+.
However, if black plays it cool on move 45 and then simply steps his king to safety or (more brazenly) to f8, he may yet still snag one of the hanging white pawns and have a chance to win the endgame with best play.
And this is where the power of being a super-elite GM comes in. DeFirmian certainly would have played the position out against anyone rated under 2400, to see if a weaker opponent could hold and not blunder. But Karpov's reputation preceded him, and probably intimidated DeFirmian into accepting a draw offer in a better position.