May 22 (UPI) -- Phil Mickelson sits atop the leaderboard after Saturday's third round of the 103rd PGA Championship and is 18 holes away from making history at the Ocean Course in Kiawah Island, S.C.
The 50-year-old Mickelson, who hasn't won a major since the 2013 British Open, is trying to become the first player 50 or older to win at a major championship. The oldest player to win a major was Julius Boros, who was 48 when he won the 1968 PGA Championship.
"I think that because I feel I'm playing really well and I have an opportunity to contend for a major championship on Sunday -- and I'm having so much fun -- that it's easier to stay in the present and not get ahead of myself," Mickelson said when asked about his mindset for the final round.
"I think that's a big part of it. ... I think we're having so much fun that it's easy to stay present."
Despite struggling on the back nine, the left-handed Mickelson shot a 2-under 70 and was at 7-under 209 for the tournament. He carries a one-shot lead over two-time PGA champion Brooks Koepka into the final round.
Mickelson, who is attempting to win his sixth major championship and second PGA title, made a 5-foot par putt on his closing hole to keep his lead through 54 holes. He had five birdies over his first 10 holes Saturday before carding a bogey on hole No. 12 and a double bogey on the 13th.
Koepka tied Mickelson for the lead with a birdie on the 16th hole, but he missed a short putt on the 18th to slip back to second at 6-under 210. Koepka had five birdies and three bogeys in his third round.
Louis Oosthuizen, who started the third day tied with Mickelson at the top of the leaderboard, was in third at 5-under par after his 72. Kevin Streelman enters Sunday in fourth at 4-under, while Branden Grace and Christiaan Bezuidenhout were tied for fifth at 3-under 213.
Meanwhile, Bryson DeChambeau sat at 2-under par for a share of seventh. He followed up his second-round 71 with another 71 on Saturday.
Sunday's final round of the PGA Championship is set to begin at 7:30 a.m. EDT.