James Hahn is in pole position to win a third PGA Tour title as he leads the AT&T Byron Nelson following a collapse by Jason Kokrak.
Hahn struck six birdies in his six-under-par 64 to sit at the top of the leaderboard on 12 under going into the final round.
Kokrak will be kicking himself after he blew a five-shot overnight lead. The American put himself in line for a first tour win with a career-best round of 62 on Friday but he went round in 10 more shots on day three, thanks in part to a triple-bogey six at the par-three fifth.
He is still in contention on Sunday, though, two shots behind Hahn and one behind second-placed Billy Horschel.
Jason Day struck the round of the day as his 63, consisting of eight birdies and a bogey, saw him surge up the leaderboard and join Kokrak on 10 under.
Defending champion Sergio Garcia will still harbour hopes of retaining his title after a 64 moved him up to eight under, but world number one Dustin Johnson looks out of contention after his one-over-par 71 saw him drift to seven shots off the lead.
Further down the leaderboard the sole Irish representative in the field, Seamus Power, shot a72 to slip back to level par.
