Rory McIlroy's slim hopes of a second US PGA Championship victory at Kiawah Island disappeared as Phil Mickelson continued his mesmerising bid to make history.
McIlroy put the finishing touches to a disappointing third round of 74 on Saturday, just as the final pair of Mickelson and Louis Oosthuizen headed to the first tee in a share of the lead.
That state of affairs did not last long however, former Open champion Oosthuizen three-putting the first before Mickelson clicked into top gear in brilliant fashion.
Aiming to surpass Julius Boros – who was 48 when he won the US PGA in 1968 – as the oldest major winner, Mickelson fired a long iron from 267 yards onto the green on the par-five second and two-putted from 15 feet for birdie.
The 50-year-old left-hander then span his approach from a fairway bunker to within two feet of the pin for a tap-in birdie on the next, holed from 17 feet for another on the sixth and two-putted the par-five seventh for a fourth gain of the day.
And with his rivals taking one step forward and one step back, Mickelson reached the turn at nine under par with a four-shot lead over Oosthuizen, Branden Grace, Masters champion Hideki Matsuyama and Brooks Koepka.
McIlroy knows all about enjoying runaway wins at Kiawah Island after storming to an eight-shot win in 2012 and, coupled with his victory in the Wells Fargo Championship a fortnight ago had seen him installed as pre-tournament favourite.
However, the 32-year-old was never a factor following an opening 75 and again failed to break par despite easier conditions on Saturday, a third round of 74 leaving the four-time major winner on five over par.
Asked what he needs to improve, McIlroy said: "It's being a little tidier around the greens, it's hitting a few more fairways, it's taking some of your chances when you do hit good iron shots, instead of making the pars, you make the birdies. Just getting some momentum.
"I just feel like I haven't had any momentum this week. When you start the way I did today with a bogey and then you don't make a birdie on the second hole, you're just always trying to play catch up, and it's hard to on this golf course because there's very few opportunities where you can be really aggressive."
Jordan Spieth might have expected to reduce his deficit to the leaders after a third round of 68 got him back to level par, but with conditions remaining favourable for the later starters, he was off to simply enjoy the Mickelson show.
"It's Phil, right. It's theatre," Spieth said. "I don't watch golf but I promise you I'm going to turn it on to watch him today. It's pretty incredible.
"He's just a great player. He's one of the best to ever play the game. He's won a World Golf Championship (event) in the last couple years and he stays relevant all the time."