By Andrew Both
KIAWAH ISLAND, S.C. (Reuters) -Phil Mickelson looked set to run away with the PGA Championship until a major stumble saw his five-shot cushion evaporate but he steadied the ship in time to sit one shot clear of Brooks Koepka after the third round on Saturday.
The 50-year-old Mickelson, who is bidding to become the oldest major winner in history, carded a two-under-par 70 that left him at seven under on the week and one shot clear of Koepka (70), who had a share of the lead until a closing bogey.
"Hopefully I'll be able to eliminate a couple of those loose swings tomorrow," said Mickelson, a five-time major champion who with a win would become the first player to go 30 years between his first and last PGA Tour victory.
"Because I'm playing a lot better than the score is showing and I think if I can just stay sharp tomorrow, I'll post a score that is -- that better reflects how I'm actually playing."
Mickelson began the day at the Ocean Course with a one-shot share of the lead with South African Louis Oosthuizen (72) but made a sizzling start with four birdies over the first seven holes and led by five shots after a birdie at the 10th.
However, things started to unravel at the par-four 12th hole where Mickelson, whose most recent major triumph came at the 2013 British Open, made his first bogey in 21 holes.
Mickelson's tee shot at the par-four 13th then found water en route to a double-bogey that left him just one shot in front of Koepka and Oosthuizen.
Four-times major champion Koepka, playing in the penultimate pairing, moved into a share of the lead with a tap-in birdie at the par-five 16th but fell one back after two-putting from about six feet at the last.
"I'm right where I want to be, and we'll see how tomorrow goes," said Koepka, who had surgery in March to fix a dislocated kneecap and ligament damage and missed the cut in his last two PGA Tour starts. "Just be within three of the lead going into the back nine and you've got a chance."
Former British Open champion Oosthuizen was alone in third place, two shots back of Mickelson.
Masters champion Matsuyama (76), in his second tournament since becoming the first Japanese man to win a major, had been in contention until a disastrous stretch that saw him cover the final eight holes in six over par.
Jordan Spieth (68), who arrived at Kiawah Island seeking a win to become only the sixth player to complete the career Grand Slam of winning golf's four major championships, struggled on the Ocean Course greens and will start the final round seven shots back in a share of 13th place.
"This is a round where I'm walking up the 18th going, man, this could have been special today," said Spieth.
Defending champion Collin Morikawa (74) was 10 shots back of Mickelson while Northern Irishman Rory McIlroy (74), who won the PGA Championship at Kiawah Island in 2012 and was a favourite to win the year's second major, was a 12 shots adrift.
(Reporting by Andrew Both; Writing by Frank Pingue; Editing by Hugh Lawson, Andrea Ricci and Daniel Wallis)