Phil Mickelson Moves to the Top of the P.G.A. Championship Leaderboard

If he triumphs at the Ocean Course on Kiawah Island this weekend, Mickelson, 50, will become the oldest winner of a major golf tournament.

KIAWAH ISLAND, S.C. — As Phil Mickelson climbed a hillock to step onto the final green of his second round at the P.G.A. Championship on Friday, a shout from the crowd rose above the growing applause: “You’re not old, Phil.” Mickelson, who will turn 51 next month, smiled and flashed a thumbs up, his favorite nonverbal acknowledgment across a career dating to the early 1990s. Minutes later, when Mickelson sank a 22-foot birdie putt that put him near the top of the leaderboard just past noon on Friday, he boyishly bounded off the green, offering a thumbs up in every direction. Eight years after his last major championship victory, Mickelson shot a 69 to finish Friday at five under par, which put him in a tie for first with Louis Oosthuizen at the midpoint of the event. Two windswept days remain on the grueling Ocean Course, but Padraig Harrington, who played in Mickelson’s group in the first two rounds, saw something distinctive in his longtime rival’s deportment.