Hideki Matsuyama produced a dazzling burst of scoring late in his first round to surge into a share of the lead at The Memorial Tournament in Ohio.
Matsuyama picked up six shots in just five holes on the back nine at Muirfield Village, a run which culminated in a hole-out for eagle from 137 yards at the 17th which swept him to seven under alongside clubhouse leaders Abraham Ancer and Joaquin Niemann.
But many of the star draws struggled on the opening day, with Justin Thomas marking his first start as world No 1 with a level-par 72, the same score as the man he replaced at the top of the world rankings, Dustin Johnson.
Tiger Woods was four over after seven holes before rallying to get back to level for the day, while Rory McIlroy (74) and Jordan Spieth (75) will need to go low early in the second round if they are to make the halfway cut.
Mexican Ancer was first into the clubhouse on seven under with a round that included six birdies in eight holes from the fifth, and the 27-year-old also birdied two of the last three to match his lowest score of the season.
He later had company at the top when rookie sensation Niemann birdied five of his first seven holes and hit back from his lone bogey at the second - his 11th - with back-to-back birdies and another at the seventh.
Muirfield Village was the venue for Matsuyama's maiden PGA Tour victory four years ago, and he put himself in contention again despite undoing his three-birdie outward 33 with consecutive bogeys at 10 and 11.
But the 26-year-old holed from 15 feet at the 13th, clipped a wedge to tap-in range at the next and converted further chances at 15 and 16 before his perfect wedge approach to the 17th pitched just beyond the pin and spun back into the cup for a rare eagle-two.
Matsuyama was agonisingly close to making yet another birdie at the last as he settled for a share of the lead, one ahead of Beau Hossler and two clear of Jamie Lovemark, Grayson Murray, Kyle Stanley and former US Open champion Lucas Glover.
Jason Day is a further stroke off the pace after being unable to build on a flying start as he birdied four of the first six holes, while last week's Forth Worth Invitational did well to get under the card after being two over early on.
Justin Rose, the 2010 champion, started his recovery with a birdie at the 18th - his ninth - and he made three in four holes on the front nine before finishing on a disappointing note as he three-putted his last green to sign for a 71.
Woods was hampered by a stiff back as he found water at his second hole and then drove out-of-bounds at the 15th, but he also staged a rally and reeled off three straight birdies on the front nine to claw his way back to level par alongside the top two players in the world rankings.
McIlroy was making steady, if unspectacular progress and made his second birdie of day with a nice approach to six feet at the 13th, but he pulled his next tee shot into water and compounded the error with a careless three-putt, missing his bogey attempt from barely two feet.
He steadied himself with a run of pars before pulling another drive into water at the last, although he did well to limit the damage to a bogey as he ended the day nine strokes behind the leaders.
And Spieth ruined a bright start with two double-bogeys in the space of three holes at the seventh and ninth, and he followed McIlroy into the left hazard at the 18th to finish off an erratic day on three over par.