England's Harry Hall fired a four-under-par 66 to take a three-shot lead at the halfway stage of the PGA Tour's Charles Schwab Challenge in Texas on Friday.

Hall, ranked 197th in the world and chasing a first-ever win on the PGA Tour, recovered from a shaky start to rattle off a string of birdies at Colonial Country Club in Fort Worth and head into the weekend at 12 under.

The 25-year-old from Cornwall had surged into the first-round lead after a flawless eight-under-par on Thursday.

Teeing off on the back nine on Friday, Hall bogeyed his fourth hole of the day but then birdied five of his next six holes to get his round back on track.

Although a bogey on the third dropped him to three under for the round, he coolly rolled in an 11-footer for birdie on the seventh on the way to his four-under round.

"I don't think I've played my best golf this year on the PGA Tour yet, and I think it's arrived this week," Hall said.

"Hopefully I can keep it going for the next two days."

Harris English is leading the pursuit of Hall after matching the Englishman's four-under-par 66, leaving him on nine under, three off the lead.

The highlight of a bogey-free round for English came with a brilliant ace on the par-three eighth, where his nine-iron off the tee landed on the green and rolled into the hole.

"It came off just like I wanted to and luckily went in the hole," English said.

"As long as I keep that ball striking going and keep giving myself chances, then some good things will happen this weekend."

Argentina's Emiliano Grillo was a further shot back on eight under after a five-under par 65, while three players — Adam Schenk, Robby Shelton and South Korea's An Byeong-hun — were five off the lead on seven under.

World No. 1 Scottie Scheffler is also in the hunt after posting a second straight 67. Scheffler was tied for seventh alongside Andre Novak on six under.

"I wish I was a little bit further up on the leaderboard, obviously, but I feel like my game is in a really good spot, so excited for the next couple days," Scheffler said.