It’s a measure of Rory McIlroy’s talent that even when struggling with his game, juggling several swing thoughts and adjusting to a new grip, he shot a level par 71 to end the day just five shots off the lead.

The world No 4 had four birdies and four bogeys in an adventurous start to the 100th Open de France where Lucas Bjerregaard took command at Le Golf National thanks to a career first hole in one with a brand new set of golf clubs as he opened with a superb 66.

The Dane had made just three of his last ten cuts but he found his form on the biggest stage with an elite field gathered at the course where the Ryder Cup will be held in 2018.

He made the 26th hole-in-one of the European Tour season on the second hole as he signed for a five under par 66 and would not be caught on a day of sun and occasional showers in Paris.

But while he goes in search of a first European Tour title, defending champion Bernd Wiesberger, Thongchai Jaidee and Thomas Pieters - who all sat just a shot back - have 12 between them.

McIlroy revealed that he is working hard to get his swing back into the groove for The Open and a change in his grip, which had become too strong, just added to the difficulty on a day when the rest of the Irish struggled.

Padraig Harrington made two double bogeys in his last three holes (and three in all) to turn a possible 68 or 69 into a 73 as Darren Clarke shot 74, Michael Hoey and Paul Dunne 77s and Graeme McDowell a worrying 80.

“There was a little bit of adventure in there, four bogeys, four birdies,” McIlroy said. “There was quite a few good shots in there which I was pleased with, a few loose ones, as well. With what I've been doing on my golf swing and trying to work on it a bit, that's to be expected, first round back. 

“But I felt like I saw some good signs out there today. Held some nice putts. Hit some good iron shots. So it's slowly coming together.”

McIlroy noticed his swing was off kilter at the US Open but didn’t have time there to remedy it and missed the cut.

Summing up the things he is working to correct, he said: “My left-hand grip is too strong. Takeaway was going on the inside. Wasn't holding my right elbow properly at the top of my swing. I wasn't getting my right knee out of the way on the downswing, so yeah, I've been working on a few things. 

“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. I felt I did okay.

“I've got another hopefully three competitive rounds here. I've got all next week, and then obviously a few days leading up to the Thursday of The Open. So hopefully by then, it will be all bedded in. I think the hardest thing is I haven't focused on my grip.

"I changed my grip when I was maybe 12 years old and I've played with it since. But it's progressively the left hand got a bit stronger and stronger, and that clubface is coming in closed at impact. Gripping the club feels quite strange at the minute but I just need to stay with it – it's the right thing to do.”

Harrington played well to be two under with three to play but ran up a double bogey six at the seventh, his 16th, when he pulled a fairway wood into deep rough off the tee.

Then at the par-five ninth, he overhit a pitch from short of the green and left himself a difficult recovery, taking four more to get down as he closed with a seven.

McDowell hit just five fairways and eight greens in regulation and had 33 putts in his 80 as he chases double Ryder Cup points and an automatic place in Clarke’s European team.

As for McIlroy, he has no fears that he is running out of time to be ready to contend for The Open.

"I hope so. I've got another hopefully three competitive rounds here. I've got all next week, and then obviously a few days leading up to the Thursday of The Open," he said.

"So hopefully by then, it will be all bedded in. I think the hardest thing is I haven't focused on my grip."

He added: " just have to keep trying to get my left hand -- my right hand is fine. I was getting a little bit this way with it. I was wondering why clubface was coming in shut at impact, and then felt a little strange.

"It's something that's hard to work. It's one of those things that you know it's going to feel uncomfortable for a while. It needed to be done and need to get it back to neutral obviously.

"As I said yesterday, Michael and I have done a good bit of work over the last few days, trying to bed some stuff in. It will take awhile but I was encouraged with some of the shots I hit out there today.

"As I said, there was a lot of good shots out there, and I think it's sometimes nice, as well, coming off a bad result like the U.S. Open, it's nice to not -- not really focusing on what I'm scoring out there and what I'm shooting and where I am on the leaderboard.

I'm just focusing on making sure I can get all these things right, all the little checkpoints I have in my swing at the minute. It's a nice thing to have. You can take the pressure off a bit. You can just go out and play and try to make a good swing every time you're over the ball.

"I didn't know what to expect. It's been a week of tinkering with my swing and stuff. I was joking with my friends at the weekend: I've got 17 swing thoughts down to about five, so I'm doing okay. Try to get that to two next week.

"They are not major changes. They are tweaks trying to get it back to where I know I can be or know I was. I'm just trying to get the swing back to where I know it can be. It's not like I'm trying to overhaul my swing. I'm just trying to get it back; if I have a blueprint on my swing, it's just gone a little bit off. I just need to try to get it back to the centre line."

What better place that Le Golf National to winkle out any weaknesses in technique.

"Better than The Open I guess. So yeah, it's a tough golf course. It puts you under pressure on a lot of golf shots. Yeah, I mean, there's no better place to test yourself than on a tough golf course where you have to keep it in play. It's not a bad place. There's not any right time to do it. Every tournament is important and you want to try and play well but sometimes it just has to be done."

Round one scores:

66 L Bjerregaard(Den);

67 T Jaidee (Tha); B Wiesberger(Aut); T Pieters(Bel); A Otaegui(Esp);

68 M Decottignies-Lafon (Fra); C Hanson (Eng); E Molinari(Ita); F Molinari (Ita);

69 A Sullivan (Eng); G Bourdy (Fra); J Luiten (Ned); R Wattel(Fra); L Jensen (Den); M Ilonen(Fin); S Gros (Fra); B Stone (RSA);

70 M Lorenzo-Vera(Fra); M Carlsson(Swe); A Saddier (Fra); J Quesne(Fra); C Wood(Eng); E De La Riva(Esp); N Colsaerts(Bel); J Hansen(Den); T Merritt (USA); A Hansen (Den); M Southgate(Eng);

71 P Meesawat(Tha); J Walters (RSA); V Dubuisson(Fra); G Boyd(Eng); J Van Zyl (RSA); C Shinkwin (Eng); T Fisher Jnr (RSA); J Wang (Kor); Rory McIlroy (Nir); E Pepperell (Eng); B Dredge (Wal); L Slattery (Eng); F Daux (Fra); J Carlsson (Swe); R Dinwiddie(Eng); M Siem(Ger);

72 A Levy (Fra); G Havret(Fra); R Karlsson (Swe); A Noren(Swe); R Langasque(Fra); J Parry (Eng); T Detry(Bel); D Brooks (Eng); G Stal(Fra); O Wilson (Eng); C Berardo (Fra); D Im (USA); C Paisley(Eng); F Zanotti (Par); M Manassero (Ita); N Elvira(Esp); B Nicolay(Fra);

73 R Cabrera Bello (Esp); R Kakko(Fin); P Harrington (Irl); D Lipsky (USA); S Hend (Aus); J Lagergren (Swe); R Ramsay(Sco); J McLeary(Sco); T Hatton (Eng); E Goya (Arg); J Campillo (Esp); L Donald(Eng); J Gonnet(Fra); T Fleetwood(Eng); S Khan (Eng); R Fisher (Eng); C Sordet(Fra); J Scrivener (Aus); R Gouveia (Por); J Gandon (am) (Fra);

74 B Hebert(Fra); B Åkesson (Swe); O Fisher(Eng); A McArthur(Sco); D Clarke (Nir); A Wall (Eng); M Pavon (Fra); D Fichardt (RSA); M Fitzpatrick(Eng); T Linard (Fra); D Howell (Eng); A Quiros(Esp); M Warren (Sco); M Kaymer (Ger); L Westwood (Eng); M Korhonen (Fin); D Dixon (Eng); T Bjørn (Den); Y Yang (Kor);

75 A Dodt (Aus); J Winther (Den); D Willett(Eng); S Webster (Eng); D Drysdale (Sco); D Horsey (Eng); R Green (Aus); W Ashun (Chn); S Jamieson(Sco); P Hanson (Swe); L Haotong (Chn); J Morrison(Eng); N Fasth (Swe); D Papadatos (Aus); R Jacquelin (Fra); M Kieffer (Ger); C Farrelly (Eng); R McEvoy(Eng); M Baldwin (Eng);

76 G Storm(Eng); M Ford (Eng); K Broberg (Swe); M Madsen(Den); B Virto (Esp); M Weir (Can); C Lee (Sco); R Davies (Wal); R Sterne(RSA); S Chawrasia (Ind);

77 F Aguilar (Chi); D Perrier (Fra); P Edberg (Swe); A Cañizares(Esp); P Larrazábal (Esp); Paul Dunne (Irl); J Donaldson (Wal); Michael Hoey (Nir); R Karlberg(Swe); S Lee (Kor); S Kapur (Ind); R Bland (Eng);

78 H Porteous (RSA); B Rumford (Aus); F Dauchez (Fra); R Paratore (Ita); S Dyson(Eng);

79 A Widemann (Fra); J Jeong (Kor); J Fahrbring (Swe);

80 N Bertasio (Ita); T Olesen (Den); Graeme McDowell(Nir); E España (Fra); R Rock (Eng);

82 B Evans(Eng);

89 J Clément(Sui);