DeChambeau mixed six birdies with two bogeys to post a four-under 66 at Oak Hill Country Club, where the start was delayed by an hour and 50 minutes due to frost and left most of the afternoon wave unable to finish before darkness.

Eric Cole fired three consecutive birdies to move into the solo lead before play was suspended at 8.30pm local time (1.30am BST) due to darkness, with the 34-year-old PGA Tour rookie having four holes left of his round to complete on Friday morning.

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Dustin Johnson was level alongside DeChambeau until carding his only bogey of the day at the par-four last, dropping him back to three under, while Adam Scott also looked set for a share of the clubhouse lead until a final-hole double bogey.

Johnson is tied at three under with Corey Conners and world No 2 Scottie Scheffler, who carded the first bogey-free round of his major career, with Scott three back at two-under alongside Viktor Hovland, Ryan Fox and former champion Keegan Bradley.

How DeChambeau set clubhouse target

DeChambeau cancelled out a three-putt bogey at the 12th by rolling in from 15 feet at the 14th and holing from a similar distance to save par from the fringe at the next, only to cancel out a tap-in birdie at the 16th by bogeying the next.

The former US Open action posted back-to-back birdies around the turn and took advantage of the par-five fourth, with DeChambeau then picking up a shot at the sixth and finishing with three pars to set the clubhouse target.

"It's a fantastic round of golf at Oak Hill," DeChambeau said. "I was looking at it throughout the week and was like, 'man, I don't know how shooting under par is even possible out here on some of the golf holes'.

"Luckily, I was able to play some really good golf, hit a lot of fairways, did my job and made some putts."

Cole made his late charge with three consecutive birdies from the second and will resume from the sixth fairway when play resumes on Friday, with the American one of 30 players still to finish their opening rounds.

Who struggled at Oak Hill?

McIlroy battled illness, erratic driving and a cold putter to salvage a one-over 71, with the four-time major champion holing a 35-foot putt for par from the bottom of a slope at the par-four second to kickstart an improved finish.

"Just not at my best," McIlroy admitted. "I'm just struggling with my swing. Yeah, it's pretty messy out there, so just trying to make pars. There was a lot of crosswinds off tees, so it made it hard to hit fairways. I can definitely hit it better than that."

Open champion Cameron Smith, Brooks Koepka and defending champion Justin Thomas all posted opening 72s, with early leader Kazuki Higa also on the same total after cancelling out four consecutive birdies early in his round by dropping five shots over his last four holes.

In contrast to Higa, Tony Finau and Xander Schauffele overcame disastrous starts to also finish two over for the day. Finau had been six over at the turn, while Schauffele had dropped four shots in his opening three holes.

Jordan Spieth began his bid to complete the career Grand Slam with a three-over 73, having come into the event with a wrist injury, while Rahm has left himself a battle to make the cut after equalling the second-highest opening round of his PGA Tour career.

Rahm racked up five bogeys in a six-hole stretch on his way to a first-round 76, leaving him 11 strokes behind Cole alongside US Open champion Matt Fitzpatrick and last week's AT&T Byron Nelson winner Jason Day.

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