SAINT-QUENTIN-EN-YVELINES, France (AFP) - Rory McIlroy had a stop-start opening to the 100th French Open at Golf National on Thursday, as Dane Lucas Bjerregaard fired a hole-in-one and opened up a one-shot clubhouse lead.
World number four McIlroy managed four birdies against four bogeys in an even par round of 71 to sit five adrift of the early lead.
Englishmen Lee Westwood and Danny Willett, playing together as they did during the final round of the latter's triumphant Masters campaign, both struggled and have work to do to avoid the cut.
Starting on the 10th, consecutive birdies at 14 and 15 got four-time major champion McIlroy off to a quick start, but he handed them back on the front nine.
Despite not being a spectacular opening to his first visit here since 2010, it was a good return for McIlroy after missing the US Open cut at Oakmont, despite two shots finding the water.
The Northern Irishman was focusing on getting his swing in good technical order, with some doubts creeping in during the round.
"Conditions were pretty tricky with the wind up and there were a couple of mistakes and loose shots in there," he said.
"I've got about four or five swing thoughts out there at the minute, so that's why I'm sort of happy with 71 with how much I'm focusing on my golf swing and my technique."
Bjerregaard's magical moment came on the par-three second hole, and he backed it up with five further birdies.
The 24-year-old had to overcome the nuisance of losing his clubs on the flight to France, although will probably consider keeping his new ones after a sparkling five-under-par 66.
He holds a narrow advantage over Belgian Thomas Pieters, defending champion Bernd Wiesberger and Thailand's Thongchai Jaidee.
World number nine Willett only had one birdie all day, although he did play the back nine in one under par to sign for a 73.
Westwood failed to bounce back from his collapse on the Sunday of the US Open less than a fortnight ago, as the 43-year-old fell away after an opening birdie to sit on three over par.
Westwood is just outside the automatic places for Europe's Ryder Cup team, so a high finish in this tournament that offers double points for the European and world lists would help captain Darren Clarke avoid a difficult decision with his wildcard picks.
Clarke accepted that with the weeks ticking past, he is keeping a close eye on all the Ryder Cup contenders.
"Obviously this week here with double points I'm watching the scoreboard closely, a lot of things can change," the 2011 British Open champion said.
"There's quite a few of those guys who are now in almost unassailable positions, but of course there's a few positions that look available.
"It will be very interesting to see this week."
Wiesberger showed that last year's three-stroke victory was no fluke with an excellent 67, but the Austrian narrowly missed a birdie putt on the 18th hole that would have given him a tie for the lead.