After throwing away a one-shot lead with two holes to play, American Justin Leonard rolled in a 19-foot birdie putt to win his 12th PGA Tour title in a play-off for the St. Jude Championship last night.

Leonard, who had previously triumphed at the TPC Southwind in 2005, edged out Australian Robert Allenby and Masters champion Trevor Immelman of South Africa at the second extra hole, the par-three 11th.

Allenby, who had won all 10 of his previous play-offs in tournaments worldwide, missed his birdie attempt from 22 feet before Immelman failed to sink his from 11.

The trio had finished the 72 regulation holes at four-under-par 276 on a difficult day of scoring with hot, swirling breezes and tight pin positions.

Leonard, who claimed the outright lead with a birdie at the par-four 15th, closed with a 68, Allenby carded 65 and Immelman spectacularly finished birdie-birdie-birdie for a 69.

Having flirted with the cut during the second round, Padraig Harrington shot a 66 brought that was good enough to share fourth with Sergio Garcia (66), Boo Weekley (68) and Alex Cejka (70).

"It's been a great week and it's very nice to come out on top," Leonard told reporters after earning the winner's cheque for $1.08 million. "I've kind of been back in the pack a little bit and was able to shoot a really solid round. I was able to hit  some good shots in the playoff and make a nice putt there at 11."

With temperatures peaking at around 95 degrees (34 Celsius) and winds gusting up to 35 kph, the top of the scoreboard fluctuated wildly in the final round.

Eight players held at least a share of the lead before Leonard appeared to have the title in his grasp when he edged one shot clear at the 15th.

A superb wedge approach to a couple of feet set up his third birdie of the round and he maintained that cushion before stumbling with a bogey at the par-four 17th.

He pushed his tee shot there behind a tree in the right rough and was forced to chip out sideways for his second shot.

After striking his third to 15 feet, he missed the par putt to drop back into a three-way tie for the lead with Allenby, already in the clubhouse, and Australian Gavin Coles.

Leonard narrowly missed out on a birdie at the par-four last where he delivered a perfect drive and an approach to 15 feet. His birdie putt slid past the left edge before he tapped in to join Allenby at four under.

"I thought I made the (birdie) putt when the ball was halfway there, unfortunately it didn't go in," Leonard said.

Coles, a 39-year-old from New South Wales bidding for his maiden PGA Tour title, fell out of the play-off when he double-bogeyed the final hole for a 71.

Immelman, playing in the final pairing with overnight leader and fellow South African Tim Clark, booked his play-off spot with his scintillating finish.

A birdie at the par-five 16th lifted him to two under before he rammed in putts from 12 and 25 feet on the last two holes.

"It was so nice to get back the feeling that I've got a chance to win, my game is coming together somewhat for next week," Immelman said, referring to the US Open at Torrey Pines starting on Thursday.