Adam Scott survived an errant drive into the lake on the 18th hole to win the Shell Houston Open, the Australian claiming the last tournament before the US Masters by three strokes after a closing six-under 66.

Holding a one-stroke lead, Scott plunked his drive into the water to open the door for defending champion Stuart Appleby to force a playoff, but his compatriot could only fire his first shot into a bunker before finding the water with his second.

"I was trying not to be down on myself," a smiling Scott told reporters after claiming a fifth PGA Tour title.

"Then obviously Stuey (Appleby) hit a poor shot out of the bunker and I was feeling pretty good again. It was a crazy finish."

The third member of their group, Jeff Maggert, also hit into the water.

The damp finish ended a day-long, head-to-head duel in which the Australian duo opened at 11-under-par, two shots behind third-round leader Bubba Watson.

They each reeled off four birdies on the front nine to pass Watson and traded the lead before Scott moved clear when Appleby bogeyed 14 and 16 to fall two shots back.

Appleby sank a 13-foot birdie putt at 17 to get within a stroke of Scott and appeared to be in good shape to at least tie for the lead his playing partner's drive went left into a lake that extends along the 18th fairway.

But when Appleby yanked his second shot into the same lake, he flung his club in frustration.

"It was a tough shot, it was a tough hole," he said.

After Appleby's collapse, Scott ended up rolling in a 48-foot putt for par to finish at 17-under-par for the tournament.

Appleby double-bogeyed to close with a 69, in a tie with Watson for second at 14-under. Watson shot even-par 72 on the day.

Scott (26) was playing in only his fifth tournament of the year in what he has described as a strategy to save his energy for the majors.

The Houston win was a good warm-up for Augusta, partly because of similarities between the two courses and the intense competition, Scott said.

"It's good to just feel the juice flowing a little bit," he said  "I feel really great about my game. I'm certainly not predicting a win at Augusta next week, although I'm feeling better now going into than I did at the start of the week."

Ireland's Padraig Harrington tied in 24th position.  The Dubliner carded a closing round level par 72 to finish on seven-under par, ten off Scott's winning total.  Reuters