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Lee Westwood left the rest of the big names trailing as he surged in front after a difficult first day of the Masters.

England's world number three fired a five-under-par 67 to lead by one from 2010 Open champion Louis Oosthuizen and Ryder Cup team-mate Peter Hanson of Sweden at Augusta.

Another former Open champion, Paul Lawrie of Scotland, shot 69 to share fourth with Spain's Miguel Angel Jimenez, Italian Francesco Molinari and Americans Ben Crane, Jason Dufner and Bubba Watson.

Rory McIlroy carded a 71, Tiger Woods 72, and Phil Mickelson 74 but Luke Donald escaped a possible disqualification after a scorecard error was eventually blamed on an administrative hiccup.

Donald shot 75 but 73 appeared on official scoreboards and it seemed for a spell that the world number one would be disqualified for signing for a wrong score.

After an investigation, Augusta officials blamed the discrepancy on a fax machine smudging the number five for his bogey on the fifth, leading to a three being inputted into the scoring system.

As the rest of the fancied "big five" - Woods, McIlroy, Donald and Mickelson - appeared to be struggling, and with mud sticking to balls from the soft conditions and tough first-day pin positions, Westwood edged ahead in imperious fashion.

The 38-year-old, who led the Masters after the third round in 2010 but was eclipsed by Mickelson's brilliance in the final round, went out in 32 with a run of four birdies from the fifth.

He dropped a shot at the 10th but got it back on the long 13th and grabbed a final birdie on the 17th.

"There was no weakness out there in my game," said Westwood, who tied his lowest round at the Masters. "I hit it close, hit a lot of fairways and rolled in some nice putts.

"I've been playing well all year so I was pretty confident. But trying not to let myself get carried away. I just wanted to come out and start steady and strong and play my way into the tournament, which I've done."

Four-time champion Woods, who was the favourite coming in after a recent win on the PGA Tour, blamed some old habits creeping into his new-look swing as errant drives on the second and 18th needed drops from unplayable lies.

"I hit some of the worst golf swings I've ever hit today, and that's all right," said the world number seven, who won the last of his 14 majors in 2008. "I just hung in there and grinded my way around the golf course and stayed very patient, stayed in the moment. I got a lot out of that round."

McIlroy, 22, looking to atone for last year's final-round collapse when leading by four, began ominously with a double-bogey six.

The US Open champion fought back to one under by nine, but on the 10th, the hole that sparked his trouble last year, he drove off the fairway on the right after overcompensating for the left-hand trees that caught his ball 12 months ago.

Though he rescued a par, he bogeyed the 11th and found the creek in front of the 13th green in two and ran up a bogey six. But he birdied 17 and 18 to end the day one under.

"I'm a lot more pleased coming off the golf course than if I had finished par and to come off under-par is pleasing," said the Northern Irishman.

"My perseverance and patience paid off and it was nice to finish as I did, but I'm surprised someone didn't go lower than five today."

Mickelson went out in 37 and then lost a ball in the left trees on the 10th and ran up a triple-bogey seven. But he clawed the shots back at the 13th, 15th and 18th to end two over.

"I missed the ball in the wrong spot, my short game didn't save me, I hit a bad drive on 10, but I'm only two over. I'm excited about that."

Before his scorecard scare a disappointed Donald confessed to struggling with his irons.

"I almost wanted it to start last weekend because I was hitting it so nicely," he said. Maybe I peaked a couple of days too early."

South African Oosthuizen, whose best friend Charl Schwartzel is the defending champion, virtually emulated his countryman's winning finish with four birdies in his last five holes (Schwartzel birdied the last four to win).

Lawrie, who won the Open at Carnoustie in 1999, held the early lead at four after an eagle on the 13th, another at the 15th and a birdie at the 17th before dropping back with a bogey to finish.

Sweden's Henrik Stenson was leading on six under after 15 but ran up a quadruple-bogey eight on 18 and ended one under.