Other stars include , Adam Scott, Shane Lowry, Billy Horschel, Victor Perez and Bernd Wiesberger.
It was a redux of the Travelers Championship earlier this summer, which went an astounding eight playoff holes, but this one with two of the top 10 players in the world and a lot more on the line.
Oosthuizen was five-under on his round before making his only bogey at the 18th to fall into a tie with Mickelson.
And going into the moving day, we can expect it to get even closer post-round three.
However, it became harder as the day progressed.
The greens started to settle, and judging the pace of it became a strenuous task.