Piercy scorched his way through the back nine at TPC Twin Cities to grab a two-shot lead in Blaine, Minnesota, on Thursday.

Piercy, who was among the late starters, was four shots back of the clubhouse lead when he caught fire and made six birdies over the closing eight holes en route to a nine-under 62.

Piercy, who is looking to snap a 14-month victory drought on the PGA Tour, finished two shots clear of Japan's Hideki Matsuyama and Canada's Adam Hadwin.

The American reached the turn at three-under but suddenly found another gear on the closing stretch and capped his bogey-free round with a birdie at the par-5 18th, where he rolled in a six-foot putt.

Matsuyama had four birdies after nine holes and stormed out of the turn with another four over a sizzling six-hole stretch before dropping a shot at his final hole, the par-4 9th.

RIGHT: Piercy is two shots clear of the field after the opening round of the 3M Open. PHOTO: Sam Greenwood/Getty Images.

The Japanese, who last triumphed on the PGA Tour at the 2017 WGC-Bridgestone Invitational, felt confident after his round.

"It was a good round today. Played well. Hopefully I can keep it going tomorrow and the rest of the week," Matsuyama told reporters through a translator. "I was putting very well today and that was the key to the round."

World No.1 Koepka, a four-time major champion, mixed five birdies with a lone bogey for a four-under-par 67 that left him five shots off Piercy.

Day, who hit 17 out of 18 greens in regulation, made a poor start before recovering to post a two-under par 69.

On the par-3 13th – his fourth hole – Day found the rough and then chipped onto the green before two putting for bogey.

But birdies on the 1st, 6th and 9th holes gave him a respectable 69, to join last week's winner Nate Lashley and keep him one ahead of compatriots Cameron Davis and Rod Pampling.

Among the other notables in the field are Bryson DeChambeau (66), Tony Finau (66), former Masters winner Patrick Reed (69) and five-time major winner Phil Mickelson (74).