The 36-year-old is on 14-under (130) after 36 holes, one stoke ahead of Cameron Champ (131) and two clear of Charles Howell (132).
U.S. Open champion Gary Woodland, world number two Dustin Johnson and two-times Masters champion Bubba Watson were among those that missed the cut.
"I had a real solid round," said Lashley, whose only blemish was a bogey on his second hole at the Detroit Golf Club.
"I hit a lot of fairways, hit a lot of greens. Had a lot of opportunities and made some of them, missed some of them.
"But overall, five under so it was another good day and I'm pleased with my round," said Lashley, who earned his PGA Tour card for the first time in 2018.
It looked like long-driving Champ would be the one to catch after the 24-year-old shot a blistering 28 on the front nine to grab the lead but he cooled off on the back nine and had to settle for a round of seven-under 65.
"For the first nine holes, the hole looked pretty big," he said.
"And on the backside I didn't play terrible. I just hit a few shots that limited my ability to get it close to the hole. I fought hard but missed a few putts I wish I could get back. That's how it goes."
(Reporting by Rory Carroll; Editing by Peter Rutherford )
