Jordan Spieth took advantage of benign conditions to grab the early third-round clubhouse lead at the PGA Championship on Saturday shortly before overnight co-leaders Phil Mickelson and Louis Oosthuizen teed off.

Spieth, seeking a win this week to complete a career Grand Slam of winning golf's four major championships, made his only bogey of the day at the par-three 17th after a wayward tee shot and went on to card a four-under-par 68 at the Ocean Course.

That left the three-times major champion five shots back of Mickelson, who held the outright lead after playing competitor Oosthuizen bogeyed the opening hole to slip into a share of second place with Brooks Koepka.

"Very pleased with climbing back to even. I hate being over par at a golf course. I mean, it's like my biggest pet peeve regardless of when it is in the tournament and I just hate seeing an over-par score next to my name," said Spieth.

"So it's nice to be tied with the course with a chance to beat it tomorrow."