Mickelson warns leaders to beware

BLOOMFIELD HILLS, Michigan (Reuters) - Phil Mickelson sent out a warning to the leaders after a frustrating day at the PGA Championship on Friday.

The world number two shot a second-round 73 to finish four shots behind leader J.B. Holmes.

"I think it gets more difficult in the afternoon, so the leaders are going to have a harder time tomorrow," Mickelson told reporters.

"As the greens get firmer or crustier and bumpier and the ball doesn't check and you can't hit it firm enough, all of the guys who are in the lead and the top half of the field will have a tougher course tomorrow afternoon."

Three-times major winner Mickelson, the 2005 PGA champion, echoed the view of many players that this PGA was playing as tough as the usually penal set-up for a U.S. Open.

"It's similar, very similar to what we see at Opens normally," the 38-year-old American said.

Mickelson said many factors contributed to the struggle to make par. For the second successive day, the scoring average at Oakland Hills was nearly five over.

"I think that the raking of the grain of the grass away from the green has made it very difficult," he said about preparations of the rough that made it harder to advance the ball.

"And given the fact that the greens are firm and fast, and you can't control it, you can't control your spin, it is difficult to get up-and-down," said Mickelson, a noted master of the short game. "I have really struggled around the greens."

Mickelson stopped short of calling conditions unfair.

"I've got two more rounds to go. So I've got to play this thing two more times and I don't really want to get into whether or not it's fair or what have you.

"Everybody's got to play it."

(Editing by Ed Osmond)