The 21-year-old PGA Tour rookie had consecutive birdies on Nos. 16 and 17 before a bogey on the final hole dropped him into a tie at 17-under 196. He won the 2016 NCAA individual title as a sophomore at Oregon.
Leishman shot 69 after setting a 36-hole tournament record previously shared by Tiger Woods.
Hometown star Jordan Spieth couldn’t make a move from eight shots back, shooting par 71 and falling 10 strokes behind.
Wind gusted above 25 mph at times after two rounds of calmer conditions and lower scores on the treeless, links-style layout a few miles south of downtown Dallas. The Nelson spent the previous 35 years on a more conventional venue in suburban Irving.
Kevin Na (69) and Matt Jones (68) both bogeyed the par-4 18th to finish at 13 under. Jimmy Walker shot 70 with a double bogey on the final hole that dropped him to 12 under, with Brian Gay, who bogeyed 18 for a 72.