Phil Mickelson sent out a warning to the chasing pack as he safeguarded his place at the head of the leaderboard in the 145th Open Championship at Royal Troon and insisted that he is in a better shape than ever to add to his haul of major titles.

On a miserable day on the Ayrshire coast, Mickelson, who propelled himself into the early lead with a shimmering 63 on Thursday, added a two-under 69 to his tally for a 10-under 132 and was heading into the third round with a one stroke advantage over Sweden’s Henrik Stenson.

The 46-year-old finally made his breakthrough in the majors when he won the Masters at Augusta in 2004 and the Californian has since collected a further four, including the Open at Muirfield in 2013.

Mickelson, who is aiming to become the oldest Open winner since Old Tom Morris in 1867, believes he is improving with age and declared that there is plenty more in the locker, both this week and in future years.

“The fact is that from 10 years ago, when I was playing my best golf, I’m 25 pounds lighter, I’m in better shape, I’m physically stronger than I was,” he said. “I feel better, I’m starting to hit some of the shots I did 10 years ago and I’m starting to play some of my best golf again. I don’t see any reason why I can’t continue that not just this week but for years. That’s the plan.”

Rory McIlroy, who is eight shots off the pace, backed up Mickelson’s claim and added: “I had a chance to watch Phil in round one and this morning, and it's the best I've seen him play in a long, long time.”

Mickelson finally won the Open at the 20th attempt three years ago and the Ryder Cup player believes his more relaxed frame of mind can help him recapture golf’s most cherished piece of silverware.

He said: “I don’t feel the pressure like a lot of the other players do to win the Claret Jug because I’ve already won it. That takes a lot of pressure off me. The desire to capture the Claret Jug puts a lot of pressure on and the fact I’ve done that relives a lot of it. I would love to add to that. We're only halfway done with the tournament so it's too far off to start thinking like that, but certainly there is nothing more that I would love to do.”

Stenson, with a trio of top-three finishes in the Open stretching back to 2008, came hurtling up the field with a six-under 65 to lurk just a shot of the pace heading into the closing 36 holes.

"I haven't been in contention for the last six majors and it was a big, big goal of mine to try and be up there and give myself a chance,” said the 40-year-old as he hunts down his first major title.

Jason Day, the world No 1, and Dustin Johnson, Jordan Spieth and McIlroy, the next three highest ranked players on the global order, all made the cut as did Masters champion Danny Willett. Colin Montgomerie, playing at his home course, looked set for an early exit until the cut line inched up and the 53-year-old made it on the limit.