Dustin Johnson leads the final major of the season having set the pace at Whistling Straits with an opening round of 66, six under par, good enough for a one-stroke advantage over Sweden's David Lingmerth.

Wold number one and defending champion McIlroy, playing competitively for the first time since June's US Open having damaged ankle ligaments playing football on July 4, had to be content with his one-under 71. He had missed an opportunity to close the gap on the lead at the 18th when he missed first the green with his approach shot at the 520-yard par four hole and then a 16-foot par putt.

The late-starting McIlroy had been playing in the opening round's marquee group alongside his great rival for the game's top ranking, Jordan Spieth, and Open champion Zach Johnson. And he shared the honours with Masters and US Open champion Spieth in the first of their two rounds together, the 22-year-old Texan also carding a 71 while last month's St Andrews winner Johnson trailed home with a three-over 75.

McIlroy had got off to a shaky start, driving into left rough off the first tee before the Irishman recovered sufficiently to give himself a par putt from inside 10 feet. There was a very early sign of rust as he missed the putt and bogeyed the first hole, an error compounded when both world number two Spieth and Johnson saved their pars.

McIlroy, though, bounced right back at the par-five second, his iron play showing no lack of sharpness as he drilled an excellent approach from 250 yards out to 22 feet, from where he two-putted for birdie to get back to even par.

There was an excellent up and down at the par-five fifth, McIlroy rolling up the right leg of his fuschia-coloured trousers to play an excellent shot from shallow water from well below the green.

He would, though, return to one over with a bogey at the par-four eighth. Birdies at the ninth, 11th and 16th, the latter two par-five holes, suggested the Holywood golfer was primed for a run at the lead but though the bogey at the last, McIlroy was pleased with his first day back at work.

“I felt it was good. It was a solid round of golf. Happy with the way I struck the ball,” McIlroy said.

“Obviously I was pretty nervous on the first tee. It was just getting back there, it was nice to get that opening tee shot out of the way. It wasn't the best of starts, but to hit those two shots on the second hole and make birdie, that sort of settled me down and I could get into the round.

“But I think anything under par this afternoon was a decent score. I set myself a target going into the back nine. I knew there would be a few chances, so I thought trying to shoot something under 70 was realistic.

“I sort of had a chance to do that after birdieing the 16th. I missed a good chance there on 17. Unfortunate bogey on the last, I guess. Just hit a 3-iron and held it up a little bit too much into the wind and leaked it right. But as I said, anything under par today is a good score, or this afternoon, anyway, is a good score.”

As for his left ankle, McIlroy added: “Fine, just as it is walking 18 and practicing. The exact same, no different.

“As you can see out there, the way I'm hitting the ball and the way I'm getting around the golf course, I have full confidence in it. It doesn't bother me one bit.”

It was the other Johnson, Dustin, who has set the target to beat after day one at Whistling Straits, the course on which he had let slip his chances of a maiden major victory five years ago at the 2010 PGA.

Continuing a pattern of last-round calamities that have denied him success at the 2010 US Open, the 2011 Open and this year's US Open, Johnson had incurred a two-stroke penalty on the 72nd hole having grounded his club in a waste area he had not realised was a bunker. Five years on, that was as far from his thoughts as he could make it, the 32-year-old getting off to a now customary fast start in a major with an opening six-under-par 66 during the best of the day's conditions yesterday morning in Wisconsin.

Of the late starters contending with a stiffening breeze, Johnson's early lead was threatened by just Sweden's Lingmerth, this year's Memorial champion, who had moved to within a shot of the American with a fifth birdie in the first seven holes of his round on the back nine.

He went into a tie with Johnson after a birdie at the par-four sixth but gave that shot back at the next hole and posted a 67, five under par, to take solo second place heading into Friday's second round.

Seven players, numbering Jason Day and fellow Australian Matt Jones, New Zealand's Danny Lee and a quartet of Americans in JB Holmes, Russell Henley, Matt Kuchar and Harris English, carded 68s to lie two shots off the lead.

McIlroy finished day one as the only Irishman under par with Graeme McDowell the best of the rest following a one-over 73 and 2008 PGA champion Padraig Harrington posting a four-over 76.

“I played beautiful all day,” 2010 US Open champion McDowell said. “Putting was difficult today - a lot of the greens are quite exposed and I left a lot of putts out there today.

“It was just a round of what could have been. I played the golf, I just didn’t hole the putts. I putted pretty awful to be honest.”

Shane Lowry admitted his head had been “all over the place” as the drama and emotion of his WGC-Bridgestone Invitational victory in Akron, Ohio, last Sunday night caught up with the Irishman.

That there was a hangover for the newly-installed world number 19 should not have come as a surprise but it was still disconcerting to see the Irishman shoot a 78 that will leave him on the same mark as Darren Clark, the pair now struggling to make the halfway cut in their second rounds on Friday.

Six bogeys and a double bogey were the collateral damage of success five days previously as Lowry struggling to get his game back in swing, just two birdies the highlights of a difficult opening round at Whistling Straits.

“I am a little bit disappointed but then I didn’t play very well out there and while I played lovely in practice I don’t know what it was out there today,” Lowry said.

“I also struggled with the pace of the greens but I am not going to stand here and claim being tired or anything like that, and while I did feel a little tired, it was no excuse as I made some poor decisions out there.

“My head seemed to be all over the place and I definitely wasn’t the calm fella who won at Firestone last Sunday, so it was just one of those days that things didn’t go for me and I need to get out there tomorrow and try and shoot a good score and see what happens after that.”