MANCHESTER — If Jason Thresher had any doubts about how his round at the first day of the Maine Open was going to go, it took one hole for them to be eased.

“I hit a wedge to about two feet,” he said. “Tap-in birdie, that’s a good start.”

A good start gave way to a great round, as Thresher carded a 6-under 64 to take the first-round lead at the Charlie’s Maine Open on Tuesday.

Defending champion Matt Campbell and Jason Millard are tied for second at 5 under. Geoff Sisk and Brendon Doyle are in a tie for fourth at 4 under.

Twelve players are within four shots of the lead and 23 are within five, but Thresher won’t be easy to catch. The West Suffield, Connecticut resident has been a force in state and regional opens, winning three straight in Massachusetts from 2016-18, New Hampshire’s last year and the New England Open this summer.

Thresher doesn’t have a Maine title yet, but he put himself in position with a nearly error-free round. Thresher birdied seven holes and only bogeyed one.

“I was never really in any trouble all day,” he said. “I played yesterday, and I hit a few wedge shots to within three, four feet. That doesn’t always carry over to the next day. To do that on the first hole, it gave me a lot of confidence.”

Still, Thresher is hardly planning his victory parade. He shot 65 to get into the final group in 2017, only to shoot 74 and finish out of contention.

“As far as getting off to a good start, I’ve done this for a couple of years now,” he said. “I haven’t been able to follow it up with a round under par. … Hopefully I can turn that around tomorrow.”

He’ll have a proven second-day player sitting right behind him. Campbell followed an even-par front nine with a 5-under back, allowing him to go into Wednesday only one shot off the pace. He emerged from a seven-way tie for third to win with a final-round 63 last year, and used another 63 to come all the way back from 23rd to win in 2015.

“I’ve been out on the road pretty much for 10 weeks straight. … I’m pretty exhausted. I took about eight days off and finally touched a club yesterday for the first time,” said Campbell, a Clifton Park, N.Y. resident who plays on the Korn Ferry Tour, the PGA Tour’s developmental circuit. “(But) I love it up here. It’s fun to get away, and this tournament is one of the best I think we play all year.”

Campbell got stronger as the round went on, and birdied the 15th and 16th holes before eagling the 18th.

“I like the back nine here,” he said. “Pretty much every time I play well, I shoot right around that on the back.”

Millard, who tied for fifth in this event last year, put himself in the final group with five birdies on the back and seven altogether. The Mufreesboro, Tennessee resident was dialed in on club selection after Augusta’s terrain perplexed him during Monday’s pro-am round.

“I know the golf course. It’s pretty hilly, and some of the holes, the yardages are tough to get correct,” he said. “I didn’t really get them correct on (Monday) and I learned from it.”

Millard got what he acknowledged to be a good break on his tee shot on the par-3 seventh, which allowed him to birdie the hole, improve to 2 under and add fuel to his round.

“It kind of got me going,” he said. “I think I’m just going to go with an aggressive approach tomorrow and try to make as many birdies as possible.”

Sisk carded a bogey-free round to shoot 66 and tie for fourth with Doyle, who birdied four holes on the back. The round was a relief for Sisk, who won the Open in 1996 and was a runner-up two years ago, but who has struggled in competition recently.

“(I’m) really happy with that. I played really well. I haven’t played well the last couple of months,” the Marshfield, Massachusetts resident said. “I haven’t played well in a long time, so this is nice to at least have one good round so far.”

After that is a tight pack of players who could make a run with a blistering Wednesday. Eric Egloff is alone in sixth at 3 under, while Chris Houston, Danny Yustin, Ian Thimble, Matthew Hardman and Mark Purrington — who aced the 163-yard second hole with a 9-iron — are tied for seventh at 2 under.

Nine players are tied for 12th at 1 under, including low amateurs Joe Alvarez (Biddeford), Peter Wright (Saco) and Scott Sirois (Falmouth). Pittsfield’s Gavin Dugas also shot 1 under to tie for the top score among Maine players, doing so in his professional debut.

“I hit 17 greens and only made two birdies, so it could have been a lot better,” Dugas said. “But coming in at 1 under is still not bad. I’ll take it, for sure. But hopefully tomorrow we can get the putter going and see what we can do.”

Rachel Smith and Ruby Haylock, the two women in the field, both shot 9-over 79s and made the amateur cut of 10 over or better.

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