Justin Thomas defeated fellow American Will Zalatoris by one stroke in a three-hole aggregate playoff on Sunday to win the PGA Championship at Southern Hills.

Thomas, the 2017 PGA champion captured his second major title by going two-under par in the playoff with Zalatoris on one-under.

Zalatoris and Thomas each birdied the par-5 13th. At the par-4 17th, Thomas drove the green and two-putted for birdie from 36 feet while Zalatoris chipped to seven feet but missed his birdie bid.

At the 18th hole, Zalatoris missed a 40-foot birdie try and Thomas two-putted from 26 feet, tapping in for par and the victory.

Thomas, who began the day seven strokes adrift, matched the greatest last-round comeback in PGA history, American John Mahaffey's seven-shot rally at Oakmont in 1978.

The title came after a heartbreaking last-hole collapse by Chile's Mito Pereira, who led all day only to end with a double-bogey disaster and squander the trophy.

Thomas fired a three-under-par 67 in Sunday's final round and Zalatoris, last year's Masters runner-up, shot 71 to finish 72 holes at Southern Hills deadlocked on five-under 275.

Pereira, who clung to at least a share of the lead throughout a dramatic final round, drove way right into water on the 18th hole on the way to a double bogey to tumble from the lead, shooting a 75 to share third with American Cameron Young on 276. (AFP)