Ben Crane snatched a one-shot advantage to lead ahead of rivals including Jordan Speith and Sergio Garcia after round two at the Byron Nelson.
World number two Spieth fired a five-under 65 to join Brooks Koepka and Bud Cauley in a share of the lead after the morning starters finished their rounds.
Overnight leader Sergio Garcia joined them at 11 under with a 66.
But Crane, ranked 405 in the world, moved one clear after a round of 63 which included eight birdies.
It continued the turnaround for the American who had completed his first bogey-free round in 36 attempts on Thursday.
Spieth dropped six shots in three holes as Danny Willett won the Masters in April, missing the cut at the Players Championship in his next outing.
As in the opening round, Spieth again dropped a shot on the par-three 13th in Texas, but also enjoyed six birdies.
“I took advantage of the easier holes, a couple of the long holes, I found both par fives in two and two-putted for birdies,” said Spieth, who made his PGA Tour debut at the 2010 Byron Nelson, finishing tied for 16th aged 16.
England’s Greg Owen (69) was joint 37th on four under, but Ian Poulter missed the cut after a 73 left him at level par.
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