US Tour:Phil Mickelson was well on course for back-to-back wins on the USPGA Tour when he held a one-shot lead over Charles Howell as Padraig Harrington slipped out of contention with a series of bogeys on the final nine holes in the Nissan Open in California yesterday.

Harrington had started the final round one shot behind the American but the Irishman fell away to nine-under-par. The Dubliner went to the turn in one-over-par and after picking up a shot at the 11th, dropped three in the next five holes to slip back to nine-under-par.

Mickelson was on 16 under, one stroke ahead of Howell with Robert Allenby another shot back with three holes to play.

It did not take long for Mickelson to build a lead after he made birdies on the first two holes for the second consecutive day - Mickelson has made a birdie on the first hole in all four rounds of the tournament.

He added another birdie on the fifth hole when he hit his approach shot to within four feet to pad his lead to three.

Mickelson, though, made a bogey on the ninth hole when he was short on his approach and then he chunked his chip and failed to make the 78-foot putt.

Els cut the deficit to one when he made an incredible flop shot off the left side of the 10th green to tap in from distance.

Mickelson is attempting to win his second consecutive tournament after winning the AT&T Pebble Beach National Pro-Am last week.

Harrington rued wasted opportunities after ending the third round trailing Mickelson by one stroke.

Mickelson shot a two-under-par 69 to lead the field on 13-under par, with Harrington nicely in second place a shot back.

Beem's 65, the best round of the third round, means the American lies third on 11-under-par as he chases his first title since the 2002 PGA Championship, while Allenby and Charles Howell III trail by three strokes after rounds of 68 and 69, respectively.

Harrington squandered chances to put distance between himself and his rivals. "I had a few opportunities," he said. "It would have been nice to get to 15, 16-under par, so that would have taken the field out."

Mickelson was also left to reflect on a missed opportunity to put himself in a strong position. Sitting on 15-under-par after 11 holes, bogeys at the 12th, 13th and 16th gave renewed hope to the chasing pack.

"It could have been a chance for Padraig (Harrington) and I to pull away a little bit there in the end," Mickelson said. "The three bogeys on the backside let 12 to 15 guys back in the tournament."

Meanwhile, South African Charl Schwartzel has pulled out of the 64-man field at the Accenture World Match Play Championship in Tucson, which starts on Wednesday.

The highly-promising 22 year-old, already a winner on the European Tour, was scheduled to have faced compatriot Ernie Els in the opening round.

His withdrawal brings American JJ Henry into the line-up, although as the lowest-ranked player he will face the daunting prospect of tackling world number one Tiger Woods.

The pair were, of course, Ryder Cup team-mates last September.