Tiger Woods shot a two-under par 68 on his return to competitive golf at the WGC Bridgestone Invitational at Firestone Golf and Country Club, Ohio.
Australian Adam Scott, who is caddied by Woods' former right-hand man Steve Williams, tops the leaderboard on eight-under after a bogey-free 62.
His compatriot Jason Day is one shot back on seven-under.
Woods, 35, said: "The hardest part was controlling the distances, I was hitting it so flush.
"I've got so much more speed and compression through impact. The ball's taking off and I was hitting numbers I've never hit before. It was fun."
The Northern Irishman did hole his 184-yard approach at the eighth for eagle but took 41 on the back nine, including a double bogey at 16.
USPGA champion Kaymer finished one-under, Donald and McIlroy two-under and Westwood five shots off the lead at three-under.