AP photo by Andy Clayton-King / Dustin Johnson tees off on the fourth hole at TPC Twin Cities during the first round of the PGA Tour's 3M Open on Thursday in Blaine, Minn. Johnson shot a 78 and withdrew, citing a back injury.

BLAINE, Minn. — Richy Werenski made a short birdie putt on the par-5 18th hole for an 8-under 63 and the first-round lead Thursday in the 3M Open, while Dustin Johnson withdrew because of a back injury after a 78.

The 24-year-old Werenski is winless on the PGA Tour and No. 248 in the Official World Golf Ranking. He broke a tie with Michael Thompson with his ninth and last birdie on a warm, windy afternoon at TPC Twin Cities.

Tied for third at 65 were reigning tournament champion Matthew Wolff, Tony Finau, Max Homa, Ryan Moore, Nick Watney and Xinjun Zhang.

All three Baylor School graduates who are regulars on golf's top circuit are in the field. Luke List was the best of the bunch Thursday, tied for 27th after a 68 with six birdies and three bogeys. Keith Mitchell was another stroke back and tied for 43rd, and Harris English (70) was tied for 58th in the field that shrank to 154 with the fourth-ranked Johnson's departure.

The 2016 U.S. Open champion's exit further depleted the star power of the second edition of the event that with the coronavirus pandemic shuffling the schedule moved to right after the Memorial Tournament and just before the FedEx St. Jude Invitational, the Memphis tournament that is now a World Golf Championship and will be held July 30-Aug. 2 at TPC Southwind. The week after that, the year's first major is finally ready to be played, with the PGA Championship at TPC Harding Park in San Francisco.

Of the top 25 in the world, Johnson, No. 6 Brooks Koepka, No. 12 Tommy Fleetwood and No. 17 Finau were the only entrants at the Minnesota event that — like all the others since the PGA Tour returned in June — is being played without spectators.

Johnson's victory at the Travelers Championship in Cromwell, Connecticut, last month did not spark a post-shutdown surge. After posting back-to-back 80s last week at the Memorial for the highest 36-hole score of his pro career, his first appearance at the event north of Minneapolis lasted just one round.

At the end of his first nine, Johnson started the 599-yard, dog-leg 18th hole with a solid drive off the tee. With 209 yards to get to the flag, he used his 6-iron for a shot that he described as "perfect" but was swallowed up in the pond just short of the rough.

"Hit it right at it, and never once did I think it was going to go in the water," said Johnson, who did mention his back during a brief interview after the round.

His next two tries met the same fate. Three penalty strokes later, he finally landed his ball on the green for a tap-in putt and a quadruple-bogey nine.

"Kind of the same last week," he said. "I just struggled with my iron play, and that makes it difficult."

Watney, who was the first tour player to test positive for the coronavirus, doing so ahead of the second round of the RBC Heritage on Hilton Head Island, South Carolina, failed to make the cut two weeks ago at the Workday Charity Open after a two-round score of 150. That one-off tournament was played on the same Muirfield Village Golf Club course that hosts the Memorial, but the setup changed drastically for the second event in as many weeks in Dublin, Ohio.

The 39-year-old Watney, who has five career PGA Tour victories, went back to the basics in practice last week — aim, balance, posture — while most of his peers played the Memorial. Having emerged from the anxiety and tedium of quarantine, grateful his symptoms were mild, Watney was eager to make his six birdies the focus of his interview with reporters after Thursday's round.

"I'm trying to put that to bed, get past it and hopefully play some nice golf after coming down with that," Watney said. "It's great to be up here after playing a good round as opposed to just other things."