Tiger Woods equalled the course record at the Firestone Country Club, shooting 61 to open up a seven-shot lead at the WGC-Bridgestone Invitational in Ohio.
The world number one's round of nine-under par was the joint lowest in his PGA Tour career and included seven birdies and an eagle.
Woods's putter was on fire as he picked up four shots on the first three holes, and he was threatening to break 60 for the first time when he sunk four successive birdies from the 10th.
However, he could only par the remaining five holes, including the last, where he recovered from a poor tee shot to ensure that his scorecard would remain bogey-free.
The American finished the day on 13-under, with reigning champion Keegan Bradley and Briton Chris Wood closest to him at six-under par.
