Both of the playoff participants birdied the closing hole of regulation, Mickelson doing so with a remarkable chip shot from deep rough that finished a foot from the hole and Berganio holing an eight-foot putt.
But when Berganio went for the 18th green in two in the first hole of the playoff, he came up short and his ball finished in the water. Mickelson, who hit his tee shot into a fairway bunker, laid up 80 yards from the green with his second and then hit his third shot to within six inches for a tap-in birdie that wrapped up the victory.
The win came 21 weeks after Mickelson had played his last previous round of competitive golf. He took a full five months off, during which his second daughter was born.
He skipped both the lucrative Tour Championship at the end of the 2001 season and the Mercedes Championship -- the exclusive tournament that kicked off the 2002 campaign.
Although Tiger Woods again dominated the tour in 2001, Mickelson had a chance to challenge the game's top superstar.
Mickelson finished among the top three on 11 occasions, having a realistic chance to win every one of those events. He won only two of them. He finished third in the Masters while missing putt after putt over the final two rounds, wound up second to David Toms at the PGA Championship and began the final round of the U.S. Open among the frontrunners only to shoot a 75 and finish tied for seventh.
He got his 2002 season started off right, however, by firing an 8-under 64 Sunday at the PGA West Palmer Course, equaling Baird for low round of the day.
Jerry Kelly, who won last week at the Sony Open in Hawaii for his first career victory, finished alone in fifth at 27-under 333 while those in sixth place at 334 included Justin Leonard, Kirk Triplett and 2001 rookie of the year Charles Howell III.
Mickelson became the 34th player in tour history to win 20 times. One more victory will tie him for 26th on the all-time victory list with, among others, Gary Player and Lanny Wadkins.