Bermuda - Germany's Martin Kaymer fired a six-under par 65 to seize a two-stroke lead over American Bubba Watson after Tuesday's first 18 holes of the Grand Slam of Golf.
Kaymer, the reigning US Open champion, was only one stroke off Australian Adam Scott's course record at Port Royal to grab command of the annual 36-hole matchup between the year's four major winners.
Northern Ireland's Rory McIlroy, the British Open and PGA Championship winner, was third on 69, two strokes behind Watson, who won his second Masters champion green jacket in three seasons last April at Augusta National.
Jim Furyk, who got into the field as an alternate after Scott turned down the chance to play due to a schedule conflict, was seven strokes adrift on 72.
Kaymer hit 16 greens in regulation, making an eagle and five birdies against a lone bogey.
He opened with back-to-back birdies then began to pull away with a birdie at the sixth, dropping a 120-yard approach shot two inches from the hole, and an eagle at the seventh, sending an 8-iron from 182 yards to six feet from the hole.
"I got a big bonus there on seven. It was a very good 8-iron that I hit to three or four feet," Kaymer said.
"Then I played really consistent. I think it's important on this kind of grass that you need to hit a lot of fairways. I hit a few. My putting felt good. If you make only one bogey on that golf course, you should do fairly OK."
Kaymer drove the green at the par-4 10th to open the back nine with a birdie and he answered a bogey at 13 with a birdie at the par-5 17th.
McIlroy was three-under after seven holes, but closed the front nine with back-to-back bogeys and missed a six-foot eagle putt at 17.
"I wasn't 100 percent on, that's for sure," McIlroy said. "I started pretty well, and then the two bogeys on eight and nine sort of took the wind out of my sails a little bit and I just found it hard to get going after that.
"Around the turn, there was a few sloppy shots and left myself with some difficult positions, but couple of birdies on the back nine, it was OK.
"At one point in the round, it felt like Martin was leaving us all behind, but I'm still there. Get off to a good start tomorrow, you never know what can happen."
McIlroy compared the atmosphere more to a friendly four-ball outing than the tension-packed major atmosphere all have felt simply to qualify for the event.
"It's a very relaxed atmosphere out there," McIlroy said.
"We're still concentrating, still trying to play good golf and ultimately try and win. But, yeah, it's more relaxed, you chat a little bit more."
Watson was a toned-down version of his usually talkative self.
"No, we don't really banter, like picking on each other or anything or making fun. Martin did. Every time he outdrove me he said, 'Look, I outdrove you again.' And I told him, 'I'm trying to learn how to hit the fairways like you other three guys.'
"We're just out here just talking about, when are you playing next, what are you doing, how is the family doing, what are you doing for Christmas, things like that. Just basic stuff. Just small talk. Because we're all friends."