Garcia shot a 63 and overtook Mickelson, who at one time on the front side was ahead by three shots. Garcia began the day five shots behind Mickelson, but birded five of the first seven holes, shot a 29 on the first nine, and tied it when he birdied the 13th hole.
Sergio Garcia comments on his win at the MasterCard Colonial.
Mickelson birdied the 7th hole to go to 15-under-par, three ahead of Garcia, but started to crumble with a bogey on the par-3 8th from a front bunker. He three-putted the 9th from 12 feet for another bogey, the last a 2 1/2-footer that caught the lip but kept going.
With the two players now tied at 13-under, Mickelson cracked again with a bogey at the 14th. He missed the green with his approach shot, chipped to five feet, and missed the putt, giving Garcia the lead.
Mickelson had one final opportunity, but missed another two-foot par putt on the 17th hole, dropping him two shots back of Garcia. Mickelson parred the final hole for a round of eve-par 70. he tied for second with Brian Gay, who shot 65.
It was the seventh time this year that Mickelson has finished in the top three, but he has only one win to show for it. That was at San Diego when he hit a ball out of bounds in overtime against Frank Lickliter, but Lickliter followed him with out-of-bounds ball of his own.
Garcia, who was fined for an outburst against John Paramour earlier in the year, finished the last two rounds of the Verizon Byron Nelson last week with a 64-65.
Full-field scores from the MasterCard Colonial