KIAWAH ISLAND, S.C. — The image has become familiar over the years. Phil Mickelson holes a birdie putt and drops that left fist in tempered celebration as he makes his run up the leaderboard in a major.

This was Friday at the PGA Championship, and he kept right on going until he tied for the lead with Louis Oosthuizen going into the weekend at Kiawah Island.

Even at age 50.

Tentative on the toughest stretch as he started dropping shots by missing putts, Mickelson began to look ageless with brilliant iron play and a pair of big birdies that led to a 31 on the front nine of the Ocean Course and a 3-under 69.

Oosthuizen had the best round of the week going, not so much because of his five birdies, but rather a card with no bogeys. That ended on the 18th hole that cost him the outright lead. He still had a 68 and will be in the final group Saturday.

Not to be overlooked was four-time major champion Brooks Koepka, whose two eagles were offset by four bogeys in a round of 71 that left him one shot behind.

Mickelson and Oosthuizen were at 5-under 139, the highest 36-hole score to lead the PGA Championship since the last time at Kiawah Island in 2012 when three players were at 140.

Mickelson is the oldest player to have a share of the lead at the midway point of a major since Fred Couples (52) in the 2012 Masters.

Mickelson has not won on the PGA Tour in two years. His last major championship was the 2013 British Open at Muirfield.