Branden Grace carded a six-under 66 to take a one-shot lead after the opening round of the Texas Open.
The South African, who is without a top-10 finish this year, mixed seven birdies with a bogey in a fine start at the TPC San Antonio on Thursday.
Grace is top of a congested leaderboard, with a group of four players a shot behind him and another 13 at four under.
Americans Will MacKenzie, John Huh and Stewart Cink opened with 67s to be tied for second with New Zealander Steven Alker.
Mackenzie and Huh were runners-up at the PGA Tour event in 2014 and 2012 respectively.
Huh went through bogey-free and MacKenzie's only blemish came at the par-four 10th, while Alker birdied his final three holes.
Among those at four under and tied for sixth is Graeme McDowell, the 2010 U.S. Open champion having holed seven birdies and three bogeys.
Alongside him is Bob Estes, the 51-year-old American whose first of four PGA Tour wins came at the Texas Open in 1994.
Estes, who last won in 2002, made four birdies in a consistent opening round.
Steve Marino, Shawn Stefani, Luke List, Brooks Koepka, Noh Seung-yul, Tom Hoge, Jonathan Randolph, Robby Shelton, Ken Duke, Brian Gay and Bryce Molder are also at four under.
Defending champion Charley Hoffman made a decent start, carding a one-under 71 to be tied for 55th.