Watson shot a 7-under-par 65 at the Hualalai Golf Club, finishing with an overall score of 22-under 94 in the Champions Tour event.
Couples closed with a 64, ending up at 21-under 195.
Watson's win was his first since 2008.
"Last year, I didn't win and that is the goal," Watson said. "I started off the right way this year with a win."