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American Steve Stricker equalled the lowest round in major history with a stunning 63 to set the pace on day one of the 93rd US PGA in Atlanta.

The 44-year-old world number five leads by two at seven under from countryman Jerry Kelly with former champion Shaun Micheel four under.

On a dramatic day, Tiger Woods slumped to a seven-over 77, while Rory McIlroy hurt his right wrist in a round of 70.

US Open champion McIlroy will assess whether to continue after a scan.

In sweltering conditions at Atlanta Athletic Club, Stricker missed a 10ft birdie putt on the last to miss out on the record. Instead, he became the 23rd different player to card 63 in a major, a feat which has been accomplished 25 times.

"I realised it was for 62 but didn't realise it was for history," said Stricker, who is chasing a maiden major title.

"It never really registered. I was just trying to make a birdie and never thought about the history of it. I hit a good putt. It just didn't go in."

Stricker began at the 10th and opened with three birdies in a row before adding others at the 260-yard par-three 15th and par-four 18th.

He picked up further shots at the first and the fifth to claim the first 63 in a US PGA since Woods in the second round of his 2007 victory at Southern Hills.

"I didn't know what to expect and maybe that was a good thing," said Stricker.

Woods slumped to his worst ever opening round in major history and finished with only 24 of the 156-strong field below him.

The former world number one birdied three of his first five holes to share the lead, but then came as he fought to control his swing.

McIlroy, meanwhile, and looked on the verge of withdrawing before battling through wrist pain with ice packs and heavy strapping.

The 22-year-old US Open champion was set to have an MRI scan before deciding whether he will compete in Friday's second round.

"If it is the same and I know that I'm not going to do any more damage to it, then I'll play," he said.

American Scott Verplank finished in fourth at three under with England's Simon Dyson and Italian 18-year-old Matteo Manassero in a group of eight players on two under.

Another Englishman, Brian Davis, ended one under with world number one Luke Donald at level par and second-ranked Lee Westwood one over.

Phil Mickelson also carded 71 for one over, while Open champion Darren Clarke struggled to an eight-over 78.