Wild PGA shootout begins as five share lead
Rory McIlroy of Northern Ireland catches a golf ball on the practice range during the final round of the 96th PGA Championship at Valhalla Golf Club on August 10, 2014 in Louisville, Kentucky - by Andy Lyons
Five-time major winner Mickelson, three-time major winner McIlroy, fourth-ranked Swede Stenson, British and US Open runner-up Rickie Fowler and Austrian Bernd Wiesberger were all on 12-under par in the early going at rain-softened Valhalla.
Mickelson, a three-time Masters champion who won last year's British Open and the 2005 PGA Championship, made a 30-foot birdie putt at the first hole and a 15-foot birdie putt at the third to reach 12-under.
McIlroy, meanwhile, stumbled back with a bogey at the third, missing a five-foot par putt.
Stenson birdied three of the first five holes while Ernie Els birdied six of the first 11 holes to reach 11-under, dropping a 25-footer at 11 to move within a shot of the leaders.