Kaymer, who began on the 10th tee, fired the lowest nine-hole score in Players history, a seven-under 29 on the front side at TPC Sawgrass.
"Today was a very special round," Kaymer said yesterday. "I didn't make many mistakes."
Kaymer's 63 matched Fred Couples in 1992, Greg Norman in 1994 and Roberto Castro last year for the lowest round in the tournament's 40-year history.
That moved Kaymer, the 2010 PGA Championship winner, two strokes clear of American Russell Henley with South Korean Bae sang-Moon three shots adrift in third at the $10 million event.
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Kaymer made short birdie putts at the par-5 11th and par-4 15th, but sizzled after the turn, starting with a 26-foot birdie putt at the first.
Kaymer reached the green at the par-5 second in two and tapped in for birdie, then added a 14-foot birdie at the fourth before closing with four birdies in a row.
The stellar final run included a 17-foot putt at the par-3 eighth and a tap-in birdie at the par-5 ninth after blasting out of a bunker just 20 inches from the cup.
"I knew I was playing well and felt really comfortable on the greens," Henley said. "As long as I keep feeling comfortable with the putter, I think I can putt well on these greens."
Henley opened with three birdies in the first four holes but suffered his lone stumble of the day at the par-4 seventh when his tee shot found the water on his way to a double bogey.