
Watson closed with a four-under 68 at Kiawah Island's Ocean Course, grabbing the lead with a birdie on the 14th hole after Romero, who led after the first three rounds, made a double-bogey from a sand area.
It was his first win since 1983, when he claimed his only three titles on the PGA Tour.
"It's been a long struggle, but I've had a lot of support," said Watson, who has seven children, including two sets of twins. "There's nothing like winning and there's nothing like having a great life. Now I've got both of them."
Watson, 51, finished at nine-under 279 for a two-shot win over Romero.