Swede Henrik Stenson squandered an early four-hole lead before holding off Trevor Immelman to win a marathon encounter in Thursday's second round at the WGC-Accenture Match Play Championship.

The defending champion tapped in a two-foot birdie putt at the par-four seventh to seal victory on the 25th hole of a pulsating encounter with the gritty South African.

Immelman missed a seven-footer there to keep the match alive and Stenson booked his place in Friday's third round where he will meet American Jonathan Byrd.

"I'm just happy I hung in there," Stenson, the tournament's 13th seed, told reporters at Dove Mountain's Gallery Golf Club.

"I made the putt on five when I really needed to and a great up-and-down on seven where he couldn't match that birdie."

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Stenson rolled in an 11-footer to birdie the par-five fifth, the 23rd hole of the match, to stay level with Immelman, who had struck his third shot there to four feet.

Two holes later, the South African appeared to have the advantage when he drove the green at the par-four seventh where Stenson found the left bunker off the tee.

However, the Swede splashed out to two feet to set up his birdie three while Immelman, after hitting his first putt to seven feet, horseshoed out with his birdie attempt.

MARATHON TIE

The marathon tie ended up just one shy of equalling the two longest matches in the tournament's history.

American Scott Verplank outlasted Lee Westwood over 26 holes in the opening round in 2006, matching the record set by Canada's [Images] Mike Weir with his victory over American Loren Roberts in the first round in 2003.

"I made some important three and four-footers to stay alive and he missed a couple of chances," Stenson said.

"I wouldn't have been as disappointed, I guess, if I would have lost as he is, because he had better chances than I did."

The Swede, who became the second European to win the coveted title with a 2&1 victory over holder Geoff Ogilvy of Australia in last year's final, made a strong start against Immelman.

He reeled off three birdies in the first eight holes to go four up before his opponent caught fire around the turn.

"He just started to play really, really solid and I couldn't throw that extra gear in," Stenson said.

"He made birdie on nine, 10, 12, 16 and 17 to get back to all square. That was why we ended up in playoff, not necessarily because I made a lot of bogeys."

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