Rory McIlroy birdied four of his final five holes to card a fine eight-under par 62 and open up a one-shot lead at the WGC-FedEx St Jude Invitational.
Just over a week on from missing the cut at the Open at Portrush, the Northern Irishman, who had started the day five shots off the lead, registered nine birdies and a bogey as he moved to 12 under in Memphis.
The world number three opened what was the joint-lowest round of the week with a birdie, added another on the third and then three in a row from the seventh, before finishing strong.
World number one Brooks Koepka is second after the American produced a round of 64 featuring seven birdies and one bogey.
"It is exciting," McIlroy told the European Tour. "He's (Koepka) the number one player in the world, four majors in the last three years, he's the man right now.
"I got to play with him the last couple of days and I enjoyed it. I enjoyed seeing what he can do.
"The last four missed cuts that I've had, I've finished first, second, first and 12th, I'm a quick learner. We're very fortunate in golf that there's always next week, you can respond so quickly from setbacks and failures.
"Tomorrow's a new day. Whatever happened today is great but I've got to reset and try and go again tomorrow. I think it's nice that I've seen some really good golf and I've seen some putts fall.
"I don't know if it gives you momentum but it gives you confidence going forward."
Overnight leader Matt Fitzpatrick lies third, one stroke behind Koepka, after a 69.
The Englishman bounced back from a double-bogey on the 12th and bogeys on the 13th and 15th by making successive birdies on the 16th and 17th.
When asked if he was pleased with how he fought back at the end, Fitzpatrick told Sky Sports: "Yes, definitely.
"I felt like I played pretty solid, certainly the front nine, lots of fairways and greens. I struggled a little bit in the middle of the back nine, but to get it back under par I felt was probably fair."
Australia's Marc Leishman, Sweden's Alex Noren and Spain's Jon Rahm are tied in fourth at nine under.
Fitzpatrick's compatriot Ian Poulter is among a trio a shot further back, along with Thorbjorn Olesen of Norway and US player Billy Horschel.
And another Englishman, Tommy Fleetwood, is one of four players on seven under. He is joined by Americans Justin Thomas, Bubba Watson and Webb Simpson.
