Mickelson started the round with a one-stroke lead over David Berganio, Jr., after shooting a personal-best 61 on the par-70 TPC at River Highlands on Saturday.
It marked the fourth time this season Mickelson had held at least a share of the lead entering the final round. He failed to produce victory in his three prior attempts.
This time, however, Mickelson was successful.
Mickelson comments on his win at the GHO
He didnt touch a club last week after shooting a final-round 75 in the U.S. Open. Instead he focused on his mental approach, practicing visualization techniques he learned at Arizona State.
Changing my outlook heading into the round as well as during the round has allowed me to perform at a higher level ' to perform my best, Mickelson said.
I feel if I can start to work on that and refine that and get better at it, I should be able to close more on the opportunities that I have been giving myself.
Mickelson finished the tournament at 16-under-par 264. Andrade shot 66 to finish at 15-under. Dudley Hart fired a 63 to tie Berganio (69) and Chris DiMarco (68) for third place at 14-under.
Tee times were pushed up on Sunday due to the threat of rain and lightning. The players were grouped in threesomes rather than twosomes and started on both the 1st and 10th tees.
Making his first tournament appearance since 1994, Mickelson made the turn in 3-under 32 to take a three-shot advantage at 17-under-par.
In control throughout the first half of the back nine, Mickelson ran into trouble when his drive on the 296-yard par-4 15th bounced into the water on the left side of the green. He chipped to 20 feet and two-putted to save bogey and maintain a two-shot lead.
Andrade, a Rhode Island native, closed to within one by sinking a 25-foot birdie putt on the 72nd hole. But his hopes faded when Mickelson two-putted the 18th for par and the victory.
This is Andrades second consecutive top-3 finish, having tied for third in last weeks Buick Classic.
Im a little disappointed that I didnt get the job accomplished in winning here, Andrade said. Usually most people dont remember who finishes second.
Mickelson has finished runner-up three times this year. This is his second victory of the season (Buick Invitational), and his ninth top-3 finish. He earned $558,000 for his 19th career PGA Tour title.
Full-field scores from the Canon Greater Hartford Open