Shane Lowry made the ideal start to his bid for a second Open title as Rory McIlroy effectively wrote off his chances of doing the same at Royal Troon.

Lowry carded a flawless 66 to hold a two-shot lead over former world number one Justin Thomas after McIlroy struggled to an opening 78.

It was a contrast which immediately brought to mind the 2019 Open at Royal Portrush, when Lowry started with a 67 on his way to the Claret Jug and McIlroy’s chances were blown away with a 79.

“It was enjoyable,” Lowry, who made birdies on the fourth, seventh, eighth, 11th and 18th, told Sky Sports.

“I got off to a bit of an iffy start and holed a couple of nice par putts early on and then I was off and running.

“I try not to think about it [2019] too much now. I holed a putt to go into the lead and I thought ‘It’s the first time I’ve led The Open in five years’.

“No matter what I do that week in Portrush will always have a special place in my heart. I love that place and I love this tournament.”

Shane Lowry plays out of a bunker
Shane Lowry chips out of a bunker on the 16th during day one of The Open at Royal Troon (Owen Humphreys/PA)

A downbeat Rory McIlroy had earlier dismissed his chances of mounting a challenge for a fifth major title after a costly run of holes around the turn.

McIlroy was level par after seven holes before running up a double bogey on the signature par-three eighth, the Northern Irishman’s first attempt to escape a bunker on the Postage Stamp coming back to his feet.

With the back nine playing downwind McIlroy was hopeful of repairing the damage, only to drive out of bounds on the 11th to run up another double bogey and eventually finish seven over par, 12 shots behind Lowry.

According to statistician Justin Ray, lead data analyst at KPMG Performance Insights, 87 per cent of Open winners since 1960 have been within four shots of the lead after the first round.

Spectators search for Rory McIlroy's ball
Spectators search for Rory McIlroy’s ball after he drove out of bounds on the 11th (Jane Barlow/PA)

Asked if he could make up the ground he had conceded, there was a lengthy pause before McIlroy said: “I mean, all I need to focus on is tomorrow and try to make the cut. That’s all I can focus on.”

The 35-year-old, who agonisingly missed out on an overdue fifth major title in last month’s US Open, added: “I felt like I did OK for the first part of the round and then missed the green at the Postage Stamp there and made a double.

“But still, felt like I was in reasonable enough shape being a couple over through nine, thinking that I could maybe get those couple of shots back, try to shoot even par, something like that.

“Even though the wind on the back nine was helping, it was a lot off the left. I was actually surprised how difficult I felt like the back nine played. The conditions are very difficult in a wind that we haven’t seen so far this week.

“I guess when that happens it starts to present different options and you start to think about maybe hitting a few clubs that you haven’t hit in practice. Just one of those days where I just didn’t adapt well enough to the conditions.”

Bryson DeChambeau, who edged out McIlroy at Pinehurst to win his second US Open, also found himself well down the field following a 76, although the American did at least hole from 55 feet for an eagle on the 16th.

DeChambeau’s front nine of 42 included a double bogey on the 612-yard sixth, where he could only advance his second shot a few yards from heavy rough before hitting his next onto the adjacent 13th fairway.

“It was a thick lie and I tried to hit a 7-iron out, and I didn’t get it high enough,” DeChambeau said.

“Then I tried to fade a 5-wood and it squirted off the left side of my clubface and just shot left. I’m just glad nobody got hurt.”

Thomas had set the clubhouse target on three under par thanks to birdies on the 17th and 18th, the two-time major winner’s 68 representing a 14-shot improvement on his opening round at Hoylake last year.

“I couldn’t even tell you what I was thinking or how it was then,” Thomas said when asked to compare the two rounds.

“I’m just worried about how I am now, and I’m very pleased with my game and know things are continuing to work in the right direction. I’ve just got to keep trying to play well.”

Sweden’s Alex Noren, who only secured his place in the field via a tie for 10th in the Scottish Open on Sunday, was a shot off the pace alongside American Russell Henley and Ryder Cup team-mates Justin Rose and Nicolai Hojgaard.

Rose, who had to come through a 36-hole qualifier to make it to Troon, carded two birdies and 16 pars in his bogey-free 69.