Mickelson last played at Oakland Hills as a member of the 2004 U.S. Ryder Cup team. Since then, the course has been lengthened by 400 yards, and tougher hazards and landing areas have been added.
Weve got a lot more work to do, said Mickelson, who played under the guidance of short-game coach Dave Pelz.
Mickelson is attempting to claim his first major since winning the Masters in 2006. This year, he tied for fifth at the Masters, tied for 18th at the U.S. Open and tied for 19th at the British Open.
Rick Bayliss, chief operating officer at Oakland Hills, said the tougher design was more appropriate to match the skills of PGA Tour players.
Its a different golf course, Bayliss said.
Adam Scott had never played the course, so he didnt experience many surprises during his four-hour practice round with Geoff Ogilvy.
Scott is coming off a 16th-place finish at the British Open.
I got a good look today, Scott said. Because it was quiet, we could spend as much time as we wanted out there. I think its all about learning the greens a bit. With the greens being so severe, you get a good picture in your mind of what the greens are (like).