Former champion Phil Mickelson equalled the lowest score in major championship history after agonisingly lipping out with a putt to claim the outright record in the Open Championship at Royal Troon.

Mickelson, who has not won since lifting the Claret Jug at Muirfield in 2013, needed to hole from 15 feet on the 18th to card a nine-under-par 62, only to see his attempt catch the edge of the hole and stay out.

The 46-year-old could barely believe it as he had to settle for a flawless 63 and a three-shot lead over compatriot Patrick Reed, with defending champion Zach Johnson and Martin Kaymer also five under approaching the end of their rounds.

World number four Rory McIlroy was three shot further back after an opening 69, the world number four one of the many players who made their score on the downwind front nine before struggling on the tougher inward half.

After a double bogey at the famous Postage Stamp par three, followed by a bogey two holes later at the 10th, Pádraig Harrington fought back with birdies at the 16th and 17th to post a one under par round of 70.

Things didn't go quite as well for Shane Lowry and Paul Dunne both left themselves with a lot of work to do.

For Lowry there was just one solitary birdie in a round of 78 that included six bogeys and a double bogey.

After reaching the turn in just one over par the Offalyman fell victim to the fearsome Troon back nine as he took 41 shots on the way back in to sit well off the pace at seven under.

Dunne was just one shot better following a round of 77 in which he also struggled on the final nine holes.

The 23-year-old went out in one under par and looked to be in control of his game before before unravelling with bogeys at the 11th, 14th, 15th, 17th and 18th which were compunded by a double at the 13th.

After his round the Greystones golfer – who led the championship going into the final day at St Andrews last year – revealed his recent struggled with the game and said that he’s simply not enjoying it at the moment.

But it was Mickelson, who finished a shot outside the play-off the last time the Open was staged at Troon in 2004, who was making the headlines.

He had never shot lower than 66 in the Open before, with his last such score sealing victory three years ago.

But the left-hander took advantage of the wind dropping in the afternoon to card four birdies on the front nine and four more on the back as he looks to follow in the footsteps of compatriots Arnold Palmer, Tom Weiskopf, Tom Watson, Mark Calcavecchia, Justin Leonard and Todd Hamilton in winning the Open at the Ayrshire venue.

That would make him the fourth oldest major champion ever and the oldest at the Open since Old Tom Morris, who was just two months older than Mickelson when winning in 1867.

McIlroy had reached four under par after eight holes — including a birdie on the Postage Stamp where he had taken nine in practice — but his round was in danger of unravelling when he double-bogeyed the 13th and dropped another shot on the next.

However, the 27-year-old bounced back with a birdie on the 15th and was satisfied to get his bid for a second title off to a solid start.

“I think if I would’ve stepped on the first tee and someone would have given me a 69, I probably would have taken it,” McIlroy said. “But if somebody had given me that score on the 10th, I probably wouldn’t have.

“But I knew today was a day where you had to make the most of the conditions because I don’t think we’re going to see the course like this for the rest of the week. I think the elements are going to be a bit of a challenge. But two under par, something in the 60s, it’s a solid start.

“I think you’re looking at something at around eight or 10 under par that might win this tournament and I felt like I got off to a good start in trying to achieve that.”

McIlroy's playing partner Bubba Watson was five under par after six holes before running up a triple-bogey on the eighth on his way to a 70, but the biggest damage was being done by the par-four 11th, which played the hardest hole on the course in the 2004 Open.

Mickelson admitted he felt like crying after coming so close to making history, adding: “This was pretty heartbreaking.

“I had this right in the centre of the hole with a foot to go and it was perfect speed. I don’t understand what just happened. It moved....I don’t understand.

“To have played this round and walk away feeling like I want to cry is a very awkward feeling.”

Mickelson felt he was coming into form after a closing 66 in the Scottish Open on Sunday, adding: “I noticed it last week at Castle Stuart, I knew my swing was back in plane and started to feel easy and that’s what it was like today.

“The only bad shot I hit all day was the tee shot on 18, I was fortunate to get away with it. And we had great weather. I’ve been here 11 days and I’ve never seen a day like this when the wind was calm and the sun was out.”

Philip Reid’s report from Royal Troon to follow...