After both men claimed routine pars on 18 in the play-off, Harrington hit his tee shot close and two-putted on 17 while Berger found the water off the tee and recorded a double-bogey five.

The victory, which also hands Harrington a place at the US Masters next month and sees his world ranking jump from 297 to 82, is his first on a major worldwide tour since his triumph at Oakland Hills, with his past two wins coming on the Asian Tour.

Harrington famously changed his swing shortly after winning three Majors in 13 months but the two-time Open champion believes his recent problems have been mental.

"Hopefully this isn't an isolated win," he told Sky Sports 4. "I really do believe in myself. I think I've found that mental edge that I've been lacking the last number of years.

"Hopefully I'll be able to stick with that going forward and be consistently contending because I know if I am contending, I can win."

He added: "When I get in contention I can hit the shots. The problem has been actually when I'm starting the week, middle of the road shots, easy shots, I'm just not hitting them.

"When I've got tough shots I can hit them."

Ian Poulter finished with a disappointing 74 while Patrick Reed carded a 73 to fall out of contention as the field finished their final rounds on Monday following lengthy rain delays over the weekend.

Harrington had looked to be out of the equation after a bogey on four and double on six saw him reach the turn in 38 but a run of four birdies from the 11th coupled with a collapse from Poulter gave him a share of the lead with Reed.

Reed found the water at 15 for a double bogey and another dropped shot at 16 meant Harrington stood on the 17th tee with a one-shot lead over Berger.

But he then found the water and double-bogeyed to hand Berger the lead before a clutch putt on 18 earned him a birdie and a place in the play-off.

Birdies on 17 and 18 had given Berger the clubhouse lead at six-under after a 64 but it looked unlikely that would be enough to finish top of the leaderboard when he walked off the course.

Berger had also picked up shots on one, three, four, nine and 11 with his only bogey coming when he found the water on six.

Poulter's problems began on the fifth when a wayward tee-shot saw him record a double bogey and another errant drive saw him find the water and bogey the sixth.

Back-to-back birdies on seven and eight saw him steady the ship but he was in the water again on 11 as he recorded a double bogey and his chances of victory evaporated as he was in the water twice more on 14 to record a triple.

Birdies on 17 and 18 meant he finished only one shot back of the leaders but the Englishman was left to rue a missed chance of a first strokeplay win on the PGA Tour.

Paul Casey and Russell Knox also finished on five under after closing 68s with Jamie Donaldson a shot further back.

Jeff Overton, Jim Herman and Luke Donald finished alongside Reed on three under.