Scottie Scheffler reached 16 under after a 10-under 60, taking a two-shot lead through two rounds at the Travelers Championship in Connecticut.
The world No. 1 made 11 birdies and one bogey, then missed a 26-foot birdie putt at 18 that would have given him a second career 59.
Viktor Hovland stayed closest at 14 under with a bogey-free 61, while Akshay Bhatia and Eric Cole shared third at 12 under after rounds of 62 and 65.
Matt Fitzpatrick sat at 10 under after closing with two bogeys in his last three holes, with Justin Rose and Tommy Fleetwood another shot back.
Scheffler, already a 20-time Tour winner and four-time major champion, said he does not expect to keep that pace but will focus on execution over the weekend.