GOLF PGA Grand Slam: US Masters champion Phil Mickelson tapped in a birdie on the final hole to become the fifth player in history to shoot 59 as he charged to victory in the PGA Grand Slam of Golf event in Kauai, Hawaii, on Wednesday.

The American's 13-under-par final round gave him a five-shot winning margin over Fiji's Vijay Singh in the 36-hole, four-man $1 million event that brings together the season's four major champions.

"I felt like this was a once-in-a-lifetime opportunity and I was glad when that last putt went in," said Mickelson, who picked up $400,000 with the victory.

"When I made the (45-foot birdie) putt on 16, I knew what was going on and I was really excited because I knew 18 was a birdie hole."

Mickelson's 17-under-par 127 total also matched the tournament record set by Tiger Woods in 2002.

Overnight leader Retief Goosen of South Africa fired a four-under-par 68 to finish a shot behind world number one Singh, who matched his first-round score of 66.

British Open champion Todd Hamilton of the US slumped to a disappointing three-over-par 75 for a 36-hole total of 145, 18 shots behind the winner.

A rueful Hamilton said: "I actually felt like I was in everyone's way today."

Mickelson went out in 28 and his total included 11 birdies and an eagle, yet it could have been even more impressive.

The left-handed Californian stood over a 10-foot eagle putt on the 18th hole for an unprecedented 58, but his attempt curved just left of the cup.

The world number five's previous career low round was a 61 at the Greater Hartford Open in Connecticut in 2001.

Three men in US PGA Tour history, all Americans, had previously fired a 59.

The first was Al Geiberger in the 1977 Memphis Classic. Chip Beck and David Duval then matched the feat before Sweden's Annika Sorenstam became the first woman to achieve the mark in 2001.

Mickelson confessed he was amazed to join the exclusive "59" club, the best score in professional strokeplay history.

Mickelson admitted: "It feels like a little fluke, because I wasn't really sharp, I didn't really feel like I was practising well.

"It just kind of all came together. The ball went in the hole. I didn't hit it great and somehow I shot 59."

However, Mickelson's round came in ideal conditions at the Poipu Bay Golf Course and, referring to his opportunities on the 10th and 18th holes, he admitted he could have shot a lower score.

"To me, there's not much difference between a 58 and 59," Mickelson added.

"There's a huge difference between 59 and 60. I just wanted to make sure I two-putted."