Patrick Cantlay took a step closer to a second Shriners Hospitals for Children Open title with a 66-64 opening to share the lead.
American Cantlay, a winner in Las Vegas in 2017 and runner up last year, reached the turn at six under after recording a birdie-eagle-birdie and picking up two more shots.
The remaining nine were steadier with a pair of birdies and a bogey on the par-four fourth seeing him 12 under for the tournament, tied with Brian Stuard who has carded two consecutive rounds of 65, Lucas Glover and Kevin Na.
Overnight leader Nick Taylor went around in 69 to slip five places down the leaderboard, and Australian Matt Jones moved up 38 places with a 63 to sit fifth.
Brooks Koepka, playing in his first tournament of the 2019/2020 PGA Tour having recovered following stem cell treatment in his left knee as well as a wrist problem, went round in par to sit tied for 106th.
England's Ben Taylor opened with a 67-67 for a share of 21st, while Russell Knox of Scotland carded 67 to tie for 35th on seven under.
