Phil Mickelson played himself right into contention to become the oldest major champion in history after taking the clubhouse lead on day two of the US PGA Championship.

The 50-year-old looked in good shape in his first round on Thursday and he went a step further on Friday, finding himself top of the leaderboard having gone around the Ocean Course at Kiawah Island in 69.

It meant the American was on five under for the tournament, and he was leading by two shots shortly after he had finished for the day.

For much of Friday it looked as though Branden Grace was going to be in charge, the South African sitting pretty at six under for the tournament as he stepped up to the tee on the 17th.

But he finished his round with a double-bogey and a bogey as the breezy conditions took their toll on the two holes regarded as the toughest on the entire course, meaning he walked off after his final hole three under for the tournament.

Mickelson had similar issues on the same two holes earlier in the day after starting on the 10th, though the five-time major winner only dropped two shots across the 17th and 18th – it clearly was not enough of a wobble to really impact his mood.

The 2005 US PGA Championship winner has not had a single top-10 finish on the PGA Tour this season, but he has a great chance to end that here.

Opening up on his brilliant start at Kiawah Island, he said: "Physically I've felt as good as ever, I've been able to perform to play the shots, but I haven't been able to be as present or sharp mentally to visualise the shots I want to play.

"Meditation has been a big part of me being able to play the shots I want. It's gotten more difficult as I've got older to focus. Your mind is like a muscle, you have to exercise.

"That's what I've been doing, some days playing [as many as] 40-45 holes to make sure I can concentrate longer than just 18."

Mickelson carded five birdies after the turn, playing a huge role in putting him into contention to surpass Julius Boros as the oldest ever major winner at 48 in 1968.

Additionally, he is the first man aged 50 or over to be in top-five contention after 36 holes at a major since 2013.

His form here is made all the more remarkable by the fact he needed a special exemption to even qualify for next month's US Open, given his current ranking of 115.

"I'm having a lot of fun," he added. "To play well, to know I'm playing well heading into the weekend, to be in contention, to have a good opportunity, I'm having a blast. I'm excited for the weekend."

Ian Poulter looked to be putting himself into contention as well only to fall apart in the latter stages of his round, carding four bogeys in his final five holes – he was previously six under for the day.

Similarly, overnight leader Corey Conners' dropped down to two under for the tournament thanks to a difficult three-over second round.

Meanwhile, world number one Dustin Johnson will almost certainly not be returning on Saturday as he followed up a shocking first day with comparatively poor two over on Friday, leaving him on six over.

Jordan Spieth faces a nervy wait, he sits at four over following a second-round 75.