Watson beat Englishman Paul Casey in a playoff on Sunday at TPC River Highlands in Cromwell, Connecticut.
In notching his eighth victory on the PGA Tour, left-hander Watson matched Canadian Mike Weir for second on the all-time southpaw list. Only Phil Mickelson has more left-handed wins, at 42.
“My goal always has been to get to 10 career wins,” said Watson, who has won five of six playoffs.
“In this day and age with all the talent in the world, double digits is a pretty good number.”
He beat Corey Pavin and Scott Verplank in the 2010 playoff for his first career win.
“In 2010, I proved to myself that I could win and I could win in a playoff,” Watson, 36, said.
The two-time Masters champion began the final round a shot behind 54-hole leader Brian Harman. Watson, however, started with back-to-back birdies to grab the lead and extended it with an eagle at the par-five 13th.
But Casey, playing in a group ahead, had the best round of the day going. He holed out from 126 yards to eagle the par-four third en route to a five-under 65. Casey and Watson (67) finished at 16-under 264.
Former world number three Casey has 12 official European Tour victories, but remains in search of his second PGA Tour win after his 2009 Houston Open triumph.
He and Watson both parred the first extra hole but an errant tee shot put Casey in trouble when they played the par-four 18th again.
Casey, who is married to English television presenter Pollyanna Woodward, found the greenside bunker with his second shot and then flew his sand shot over the green to make Watson's victory a formality.
Watson put his opponent out of his misery with a 10-foot birdie putt.
Harman, meanwhile, started slowly, but a birdie-birdie finish enabled him to finish third at 15-under, one shot out of the playoff.
He earned an exemption into next month's British Open at St. Andrews, as did Canadian Graham DeLaet, Swede Carl Pettersson and former world number one, Englishman Luke Donald.
Original source: Watson wins second Travelers title