Kevin Chappell became the 11th player in PGA Tour history to shoot a sub-60 round with an 11-under-par 59 in the A Military Tribute at the Greenbrier in West Virginia.
Chappell, playing his first PGA Tour event for 10 months after having back surgery last November, missed an 11-foot putt on the 18th.
Had the putt gone in he would have equalled the lowest round of 58 on the PGA Tour – shot by Jim Furyk at the Travelers Championship in 2016.
“I couldn’t be happier where I’m at or more proud of myself in what I did,” Chappell said on Sky Sports.
“Ten months ago I was on the couch and couldn’t walk. So many people had a lot to do with getting me out here and getting me competitive.
“I haven’t accomplished anything yet, there’s a long weekend ahead, but this is a step in the right direction.
“I never stopped believing but it’s nice to have the evidence and move forward.”
Californian Chappell tied Mark Calcavecchia’s PGA Tour record of nine consecutive birdies in moving to within three shots of tournament leaders Scottie Scheffler, Joaquin Niemann and Robby Shelton.
Scheffler, in just his second round as a PGA Tour member, and Niemann had shot 62s with first-round leader Shelton firing a 65.
Adam Long is one further back on 12-under at the halfway stage.
Scotland’s Martin Laird had a 68 to for a six-under total of 134, two shots inside the cut.
But Ireland’s Seamus Power missed the cut by one stroke after a second-round 69.