Jake Knapp takes control at CJ Cup Byron Nelson

Jake Knapp's second straight 7-under-par 64 vaulted him into the lead at the CJ Cup Byron Nelson on Friday in McKinney, Texas.

Starting his round on the back nine at TPC Craig Ranch, Knapp rolled in four birdies on each side, finishing with a two-putt birdie at the par-5 ninth to get him to 14-under 128. That was enough for a one-shot lead over Troy Merritt, who fired a 9-under 62 Friday, and first-round leader Matt Wallace of England (66).

Knapp, 29, is a PGA Tour rookie who broke through for an unlikely win at the Mexico Open in February. He tied for fourth the following week at the Cognizant Classic, but his results spiraled downward after that.

"I think I just got a little tired," Knapp said. "I think mentally it was just a lot going on, and I wouldn't say necessarily life changing, just everything got busier and days got longer. It was just a bit of an adjustment. Didn't feel like I had the same energy throughout the day in some of those weeks, which was kind of a bummer.

"Decided to take last week off and give myself a good reset at home and work on some things I've been struggling with, and feel like it's working out this week so far."

Merritt also started on the back nine and made the turn in 3-under 32, then picked up steam on the front nine. After four more birdies, he drained a 16-foot eagle putt at No. 9 to secure the low round of the day.

Kelly Kraft (66) is in fourth at 12 under and Keith Mitchell shot a 65 to join a tie for fifth at 11 under with Davis Riley (67) and Canada's Taylor Pendrith (67).

Defending champion Jason Day of Australia posted a 70 and was on track to make the cut on the number at 6 under. Jordan Spieth, the Dallas hometown favorite and highest-ranked player in the field at No. 20, will miss the cut at 4 under (68-70).