Matt Kuchar wins Match Play title
Four up after nine holes on a chilly afternoon of biting winds at Dove Mountain, Kuchar fended off a late Mahan fightback before sealing the win at the par-four 17th where his opponent took four shots to reach the green.
It was Kuchar's fifth triumph on the PGA Tour and his first success in one of the elite World Golf Championships (WGC) events which bring together the game's leading players.
Defending champion Mahan, who had not trailed in any of his five previous matches this week, never recovered after going three down with a run of four consecutive bogeys from the par-three third.
Both players wore balaclavas as temperatures dropped to the mid-40s (F) with a wind chill factor of 37 and Mahan faltered early, bogeying the par-four fourth after failing to reach the green in two and hitting a poor chip 20 feet short.
He also bogeyed the fifth, after taking three shots to reach the green, and the par-three sixth, where he three-putted from long range, to go three down.
Kuchar then went 4-up with a birdie at the par-five eighth, getting up and down from just off the back of the green while Mahan had to settle for a par after missing the green well to the left with his second shot.
Mahan clawed one hole back with a two-putt par at the 10th, where Kuchar bogeyed, before recording his first birdie of the round at the par-five 11th to trim his opponent's lead to 2up.
Kuchar did well to birdie the par-three 12th where Mahan's tee shot ended up just five feet from the pin, sinking a 14-footer there to stay 2up.
Both Americans failed to reach the green in two at the par-five 13th but Kuchar pitched up to five feet and coolly sank the birdie putt to regain a 3up advantage.
Mahan immediately responded, hitting a pinpoint approach to within three feet of the flag at the par-four 14th for a conceded birdie as Kuchar was again pegged back to 2up.
Though Mahan birdied the driveable par-four 15th, Kuchar matched him by sinking a slick 11-footer before coming unstuck with a bogey at the par-three 16th where his tee shot sailed into a grandstand.
Both players ended up in the right fairway bunker off the tee at the par-four 17th but Mahan, from a relatively poor lie, struck his second shot under a bush in a waste bunker short of the green.
Kuchar's approach settled within five feet of the flagstick and he watched as Mahan blasted out of the bush for his ball to advance only a few feet. After chipping up to eight feet, Mahan conceded the hole and the match.
In the consolation match, Australian Jason Day beat 2010 Match Play champion Ian Poulter of Britain 1up to secure third place.