"There is no perfect game in chess," Fischer once said. After all, we are human and we make mistakes. But the twelfth World Champion Anatoly Karpov came close to playing a mistake-free game at the 1974 chess olympiad in Nice, France. His opponent in that game was GM Lubomir Kavalek, who shows us how Karpov improved an essentially drawn position and turned it into a win.
Karpov,A - Kavalek,L game as PGN: http://www.chessbase.com/news/2011/games/kavalek45.pgn