From the Top 10 Comebacks of all time:

Gary Player had won The Masters golf tournament three times in his career, but during the 1978 version, he did not have the start he hoped for. After the third day, he was trailing the leader, Tom Watson, by an almost insurmountable seven strokes. He was sitting in 10th place. Watson won the tournament the year before and was clearly in the driver’s seat for another green jacket.

However, Gary Player had different ideas. With three other players breathing down his neck on the final day, Player made the turn at two under par and buried six birdies in his final nine holes to take the lead and the win by one stroke with an unexpected score of 64.