Keith Mitchell led a birdie spree at the Truist Championship on Thursday, shooting a career-best 9-under 61 to shatter the course record at the Philadelphia Cricket Club.

The previous Wissahickon Course record of 65 was shared by Colin St Maxen, Zac Blair and Angus Flanagan. The 7,100-yard A.W. Tillinghast design with modest par 4s and gettable pin placements fell victim to the long hitters and aggressive shots with short irons and wedges.

Mitchell was bogey-free and had an outside chance at 59 on his second shot from 102 yards on the ninth hole, his 18th. He hit his approach to just more than 9 feet and settled for a closing par and a one-shot lead over Denny McCarthy. Colin Morikawa, Rickie Fowler, Sepp Straka and Akshay Bhatia shot 63.

Rory McIlroy, making his first individual start since completing the career grand slam at the Masters, had a 66 and was one of 64 players who beat par on the seemingly defenseless Wissahickon layout in the sixth signature event of the PGA Tour season.

Mitchell led the way despite a ho-hum start of five straight pars on the back nine. Things started to heat up for the 33-year-old with birdies on the stout 17th and 18th holes. His run continued with birdies on two of the first three holes on his back nine before a four-birdie run for a 6-under 29 on the inward nine.

Mitchell said he has a buddy who is a member at Philly Cricket and received some intel ahead of his arrival. But, he credited the work he and his caddie did early in the week studying the greens for setting the stage for his success.

“I just plotted my way around Monday and Wednesday to figure out what to hit and where to kind of try to put the ball on the green,” said Mitchell, who has one career win and six top-25 finishes this year with one missed cut. “If you get above the hole really pin high on the wrong side, you can have a really fast putt and have a ton of breaks.”

McCarthy, 32, who has lost twice in playoffs and is winless on tour, was aided by a fast start that included five straight birdies at Nos. 11-15. He opened his inward nine with back-to-back birdies and added two more for a satisfying, but not surprising to him, opening round.

“I’ve been playing really well lately, so it doesn’t really surprise me,” he said. “There’s still a lot of golf left. This is a really nice start. I’m excited for how my game has been trending lately.”

McIlroy, the defending champion and four-time winner of the event, stayed with his aggressive gameplan of trying to overpower the layout with driver off the tee. He had two stumbles along the way: a three-putt at the par-4 11th and a bogey at the 570-yard, par-5 15th, where he scrambled after missing the fairway with his drive and the green with his approach from 243 yards.

Mackenzie Hughes of Canada birdied his last four holes for an 8-under 63, giving him a one-shot lead after the first round of the Myrtle Beach (S.C.) Classic.

The winner of the PGA Tour event — held opposite a signature event at the Truist Championship this week — gets a spot in the PGA Championship if not already eligible.

That’s not the case for Hughes or two of the players one shot behind him — Seamus Power and Thorbjorn Olesen of Denmark — both already in the field next week at Quail Hollow.

Will Chandler also shot 64. He has yet to qualify for the PGA Championship.

Hughes finished with a flurry, making five birdies over the last six holes. He is a two-time winner on the PGA Tour, though it has been more than two years since his last title.

He felt like his putting has let him down in recent weeks, so he changed his routine by being quicker and more instinctive on the greens.

“Putted nicely today,” he said. “Then at the end there I kind of caught fire. I can’t remember the last time I birdied the last four holes. But it’s definitely a nice finish.”

The group at 66 included 44-year-old Nick Watney, who hasn’t won in 13 years, and 17-year-old Blades Brown in his first year as a pro.

LPGA Tour

Jeeno Thitikul of Thailand feels so much better when she sees putts going in, and it was a happy occasion at the Mizuho Americas Open. She took only 26 putts, eight of them for birdie, in a clean start of 8-under 64 to lead by two shots.

Thitikul was bogey-free at Liberty National and had the advantage of playing in the morning with virtually no wind on the course across the Hudson River from Manhattan in Jersey City, N.J.

She finished strong, dropping a short iron into 5 feet on the 17th and judging the distance perfectly on the closing hole with a shot that stayed below the hole and left her only about 3 feet for birdie.

Celine Boutier of France ran off five straight birdies in the middle of her round to account for not taking advantage of the par 5s. She was at 66 with Hye-Jin Choi of South Korea and Lindy Duncan, who lost in a five-way playoff at the Chevron Championship two weeks ago.

“I think my putter working well, better than Chevron week,” said Thitikul, the No. 2 player in the women’s world ranking.

She opened with rounds of 71-75 at the Chevron Championship, the first major of the LPGA season. Thitikul took off last week and devoted a lot of time to her putting, almost to a fault. She found her emotions going all over the place depending on the result.

“First couple days I’ve been back home and I putt a lot, a ton,” she said. “I feel good when I see it drop but I feel bad when I see it miss. ... And I was like, ‘No, you can’t be like this.’ It’s in or it’s not. It has to be the same feelings and emotion.’

Defending champion Nelly Korda had six birdies — three of them on the par 5s — to account for a few bogeys on her front nine and finished in the group at 68.