Watson claimed another green jacket by shooting a 3-under 69 in the final round Sunday, fending off Jordan Spieth's bid to become the youngest major champion since 1931.
The 20-year-old Texan led by two shots heading to the eighth hole, but the tournament changed suddenly.
Watson made two straight birdies, Spieth took back-to-back bogeys - and just like that, Watson was up by two strokes at the turn.
The left-hander led the rest of the way, adding to the 2012 title he won in more spectacular fashion with a playoff victory. The winning score was 8-under 280.
Spieth finished with a 72, his worst score of the week. He was 283 overall, tied with Sweden's Jonas Blixt.