Watson survived a seven-man playoff to claim a first-place check of $240,000. His closing total was 3-under-par 69.
"It's pretty amazing," said Watson, who also won this year's Senior PGA Championship. "I thought I had the tournament in control at No. 17, but it came back to me and it feels pretty good."
Watson made a double bogey at the 17th to drop into a tie for the lead. He also made a birdie in the playoff -- which featured the largest field ever on either the PGA or Champions Tour.
All seven players ended regulation with 54-holes totals of 9-under 207.