Defending champion Sebastian Munoz of Colombia shared the lead with Americans Jimmy Walker, Charley Hoffman and Kevin Chappell after Thursday's opening round of the US PGA Sanderson Farms Championship.
All four fired eight-under par 64s in the opening round at the Country Club of Jackson (Mississippi) to share the lead. Canada's Michael Giligic and South African M.J. Daffue were on 65.
Munoz won his first PGA title last year in Jackson with a par on the first playoff hole to defeat South Korea's Im Sung-jae.
The South American, trying to become the event's first repeat winner, birdied four of his first five holes, made his lone bogey at the ninth, then ran off four birdies in a row starting at the par-3 13th.
"I just kind of tricked myself into thinking I was not the defending champion, just thinking it was another tournament at a course that I really like," Munoz said. "It has been working so far, so I'll keep doing that."
Hoffman, a four-time PGA winner but never after leading or sharing the lead in any round, reeled off four birdies in a row starting at the par-5 third.
Chasing a fifth PGA title and first since 2016, Hoffman birdied the odd-numbered holes on the back nine, including a 13-foot birdie putt at the par-3 13th and a birdie putt from just inside 22 feet at the par-4 17th.
"A few under par on this tract, I'm happy," Hoffman said. "To get 8-under is really good. I did everything well, I made some putts and that's a really good formula."
Walker hasn’t won since taking the 2016 PGA Championship for his sixth tour victory, having battled Lyme disease since 2017 and nagging elbow and shoulder pain this year, missing six of his past seven cuts.
"I haven't been playing very well, but I feel good. It just hasn't clicked yet," Walker said after a bogey-free day. "I'm seeing some putts go in."
Chappell, whose only tour title came at the 2017 Texas Open, started on the back nine and birdied four of his first six holes, then finished with back-to-back birdies.
"I'm just out there trying to play good golf. Good golf from me is good enough to play at the highest levels out here," Chappell said. "The focus is just on enjoying it and playing good golf. The results will come."
India's Anirban Lahiri and Australian Cameron Davis were in a pack sharing seventh on 66.