Open champion Harrington is having the time of his life

Harrington fought back from one over with three straight birdies from the 13th before bogeying 17 in Tulsa.

Westwood blew a share of the early lead with a late double bogey, while Sergio Garcia, three under after four, slipped back to close on level par.

Justin Rose bogeyed the last to also end level after a controlled round in fiery conditions at Southern Hills.

Interview: Padraig Harrington

Colin Montgomerie dropped from three under to two over with three straight bogeys to finish.

"A 69 in the first round of any major is going to keep you in the tournament," said Harrington.

"Obviously since I've won at the Open, things have moved very quickly. The benefit is the fact I've won a major. You feel like you've won one, you can win two, you can move on from that.

"So there's a certain level of confidence. And I also feel that there's a certain level of adrenalin coming on from having won, and a certain high from it."

Worksop's Westwood was three under after 16 holes but took two to get out of a greenside bunker on the short 17th and ran up a five en route to his 69.

"I'm quite pleased with that," said Westwood, who has never finished better than 16th in 10 previous trips to the USPGA.

It's like playing in a sauna with your clothes on Lee Westwood

"I'd have taken that before the off. It's not easy out there. I don't find it an easy golf course to play.

"Shame about the double, but you're always going to make mistakes."

Westwood, who ended two shots adrift of early clubhouse leader John Daly, likened the cloying 38C (100F) temperatures in Oklahoma to playing a tournament in Malaysia or Singapore.

"It's like playing in a sauna with your clothes on," he said.

Rose bogeyed the par-four 2nd before moving to one under with birdies on the par-three 6th and par-five 13th.

He came close to several more birdies in a decent back nine before a late mistake on the 18th cost him dear.

England's Ian Poulter will be pleased with his one-over 71, despite a bogey on the 16th frustrating his hopes of breaking par.

His compatriots Paul Casey carded a two-over-par 72 and Simon Dyson a 73, but David Howell will resume on five over with Northern Ireland's Darren Clarke a further two shots back and Nick Dougherty even worse off on +8.

Garcia watches a putt slip by in Tulsa

Spain's Garcia looked to have shrugged off the disappointment of losing out to Harrington in a play-off for last month's Open Championship.

The 27-year-old, who led the Open for three rounds at Carnoustie, was two under with two to play but dropped shots at the 8th and 9th.

"It was just a shame, those bogeys on the last two," said Garcia, who started at the 10th. "I misread both putts.

"But overall it was not a bad round. I got off to a great start and I missed three good birdie chances on 14, 15 and 16 so I could have been easily four or five under through seven.

"Then there's some tough holes coming out and I made a couple of bad bogeys here and there. I recovered nicely, though, and then unfortunately I just didn't have a great finish."

Garcia missed a 10-foot par putt on the 18th to win at Carnoustie but insisted he had recovered from the disappointment.

"On a scale of 100, there were probably 95 positive things and five negative things. So you can't forget about a week that is so positive," he said.

England's Luke Donald, fancied by many as a likely USPGA contender, dropped back-to-back shots at seven and eight but made nine straight pars coming home for two over.

"I played quite solid, 13 greens, but 33 putts undid me," Donald said.

"I am still encouraged, if I keep playing like that, they can start dropping."