Robert Allenby has magnified his reputation as golf's greatest duelist when he knocked American Bubba Watson out of a play-off to capture the Australian Masters and with it the 'Triple Crown'.

Extending his fearsome play-off record to an astonishing 9-0, Allenby won his second Masters at Huntingdale at the first extra hole and annexed his third title in as many weeks after wins in the Australian Open and Australian PGA.

Allenby, the home-town hero and Watson, who launches drives like missiles, took advantage of a disappointing back nine meltdown by West Australian Nick O'Hern, who had led from the start.

O'Hern took a three shot lead into the final round but self-destructed on the back nine with a quartet of bogeys which destroyed his hopes of scoring only his second tournament win.

Allenby, who said he had never been so nervous as in this bid for Australia's three major titles, defined his challenge with an eagle three at the 14th, sinking a 12 metre putt to join Watson in the lead.

"I was nervous on every single shot this week, and that is the absolute truth," Allenby said.

"I kept telling myself, you've got to be strong, it's a long way from Thursday morning to Sunday afternoon.

"Treat it as a marathon - you can't win the first day, you can't win the second day and you definitely can't win the third day.

"It was just a matter of hanging in there and making birdies when I needed to and try and make pars," he said.

"I knew it would come down to the end so I wasn't trying to force it, I knew if I tried to force it I'd make mistakes.

"I played in a lot of control this week ... I made a great up and down on 17. I would never want that chip ever again. I had to go over two elephants to get to the flag there," he said.

Watson, who collected eight birdies in a final round of 67, made a crucial slip with a dropped shot at the 17th.

That left him level with Allenby at 17 under the card on 271 after the pair had both scored regulation pars at the final hole.

As the Masters was sent into a play-off for the fourth straight year, Allenby and Watson retreated to the 18th to decide their fate.

Allenby had two years ago extended his play-off record to 8-0 when he seized his first Masters jacket in a four-way fight, and Watson said later he was aware of the Australian's imposing head-to-head history.

Both drove down the centre of the fairway at the first extra hole and made similar approach shots above the hole, with the American slightly closer at eight metres from the pin.

Allenby rolled his birdie attempt towards the hole but it cut away at the last moment.

He holed the short putt before Watson's ball slid about one metre past.

Coming back Watson pulled the shot and it rimmed the cup, lipping out to hand Allenby the trophy.

Three weeks ago Allenby could barely hold a club and was in doubt on the eve of the Australian Open because of a hand injury.

With constant physiotherapy he played on and won his second national championship by one shot, then took out the PGA last week before returning to Victoria to attempt a third win.

"I can't ever imagine playing three weeks of unbelievable golf, Allenby said.

"When I came down I wasn't expecting to win at all and I've walked away with three of them. It's quite remarkable.

"I didn't even think I was going to play the Australian Open, let alone win it but - (physiotherapist) Paul Trainor - I can't thank him enough, he's worked absolute wonders on me.

"It's been an amazing three weeks and I'm proud of myself for hanging in there and doing what was needed."

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