Ryan Moore reeled off four consecutive birdies to punctuate a bogey-free 65 during Thursday's first round of the Memorial Tournament in Dublin, Ohio.
Moore blitzed the Muirfield Village Golf Club for seven birdies in all to lead by one shot over Jordan Spieth. A pack of five players another shot back at 5 under par includes former major champion Martin Kaymer of Germany and Bud Cauley, who is playing the event one year after being forced to withdraw following a car accident.
Tiger Woods is five shots off the pace, but he rallied to post a 2-under 70 with three birdies over his final five holes.
Moore, a key factor in the United States' 2016 Ryder Cup victory, entered the week with little fanfare. He missed the cut at the PGA Championship, one of four missed cuts in a 2019 season that has produced only one top-15 finish for the five-time winner on the PGA Tour.
Moore, 36, got his round rolling with a birdie on No. 2, then converted four consecutive birdies on Nos. 4-7 to make the turn in 5-under 31. He added a pair of birdies on the back nine.
Spieth entered the week with strong momentum following a tie for third at the PGA and a tie for eighth at last week's Charles Schwab Challenge. Starting on the back nine, he built on that confidence with four birdies before making his turn.
After adding a birdie at No. 3, he drained a 36-foot eagle putt on the par-5 fifth hole. He would have finished the day even with Moore if not for a bogey on No. 8.
Spieth's round included only 22 putts, but he did have two chip-ins to help that number.
"One of those days I didn't necessarily play like a 6-under score, but it was still a really solid day," Spieth told reporters. "I hit almost all the fairways, maybe missed one or two of them, and from there was able to get it on the greens. If I wasn't, I was in a pretty good place most of the time. And then the putter was what I like to see.
"In the last few weeks, I've been putting pretty well. I made a long one today and kind of knocked all the ones in that I should have made."
Woods also started on the back nine but made his turn in an uninspiring even par.
"It's one of those days that could have easily flipped," he told reporters. "Like I could have gotten a few more out of it. It was close to being easily a few more under par ... It was soft enough, it was gettable. And I just didn't quite do it."
The most dramatic part to Woods' opening round was his group being put on the clock after nine holes for falling a full hole behind. Woods was playing with England's Justin Rose and defending champion Bryson DeChambeau, who has been oft-criticized for his deliberate playing style.
DeChambeau was also given a time warning with four holes to play -- another one would have resulted in a one-stroke penalty. He double-bogeyed the next hole en route to carding a 2-over 74.