Starting his final round nine under par at Whistling Straits, the German holed from six feet at the par five second and then converted another chance at the fourth.
At 11 under, he was joined by American duo Nick Watney and Dustin Johnson.
Overnight leader Watney double bogeyed the first after a duffed chip to slip from 13 under, while his big-hitting playing partner birdied the same hole.
Rory McIlroy was still in the hunt at ten under, but had twice had to produce miraculous up and downs just to stay level par for the day.
That left him level with Jason Day, with Camilo Villegas and Liang Wen-chong amongst the group on nine under.