The 25-year-old American stood on 14-under 128 after 36 bogey-free holes, having matched the course record at TPC Twin Cities in Blaine, Minnesota.

US compatriots Scott Piercy and Sam Saunders were also in the clubhouse sharing second on 132, with India's Arjun Atwal on 133.

DeChambeau made more than 137 feet of putts on Friday, when he began on the back nine. He birdied the par-5 12th, drained a 19-footer on the par-3 13th and a 21-foot putt two holes later.

Making his turn onto the front side, DeChambeau birdied six of the first eight holes.

"I made a couple more putts outside 20 feet, definitely converted on the par-5s, certainly wedging was a lot better," DeChambeau said when comparing his second round to his first.

DeChambeau said he has made a slight change that has improved his putting, keeping the change to himself.

"It has been through a lot of practice, trial and error and struggle," he said.

DeChambeau enjoyed great success in 2018, winning the Memorial tournament, the Northern Trust and Dell Technologies Championship in the US PGA playoffs and last November's Shriners Hospitals for Children Open at the start of the current campaign.

He's going for a sixth career US PGA title this week, having also taken the 2017 John Deere Classic.

It would be his second trophy of the year overall, having won the European Tour's Dubai Desert Classic in January by seven strokes.=

Piercy, who opened with a 62 Thursday to grab the 18-hole lead, endured a wild round that also began on the back nine. He answered a bogey at 11 with an eagle at 12. He then bogeyed three holes in a row before a birdie-bogey close.

Birdies at the second, fourth and sixth holes enabled Piercy to stay near the lead.

Saunders, the grandson of golf legend and course architect Arnold Palmer, sank a 33-foot birdie putt at the par-3 13th and closed with back-to-back birdies to shoot 67.

Top-ranked Brooks Koepka, a four-time major champion, shot 72 to stand on 139.