Phil Mickelson

Phil Mickelson reacts after making a birdie putt at No. 17 on Saturday during the third round of the U.S. Open. (Brendan Smialowski / AFP / Getty Images / June 15, 2013)

When everyone else wilted, Phil Mickelson hung on.

Coming down Merion Golf Club’s devious home stretch, Mickelson played a nervy game and, despite a finishing bogey, grabbed a one-stroke lead at the U.S. Open heading into Sunday.

The fact that Mickelson was the only player under par after three rounds served as testament to the difficulty of a course whose final five holes squeezed bogey after bogey out of the golfers atop the leaderboard.

“I had to be really patient not to force the issue and fight for par out there,” Mickelson said. “This is a really fun challenge. It is a hard challenge but it is really fun.”

Among the other top golfers on Saturday, Charl Schwartzel and Hunter Mahan bogeyed Nos. 17 and 18, falling into a tie for second at even par. Luke Donald gave away three strokes in those two holes to finish at one over.

“It’s all about patience, isn’t it?” Mahan said. “You’ve just got to hang in there. You’ve got to fight.”

Headed the opposite direction, Steve Stricker recorded a 32 on the back nine -- tied for best of the week -- to join Schwartzel and Mahan in second place. Donald, Justin Rose and Bill Horschel, who started the third round tied for the lead, stood tied for fifth, only two strokes back of Mickelson.

Fans cheered the Mickelson when he birdied No. 17, only the fifth player to do so all day. They cheered again as he walked up the 18th fairway, where his solid-looking second shot had the bad luck to dribble into a difficult lie just off the green.

The golfer known as “Lefty,” who just missed a par putt on the 18th, has a history of losing tournaments at the very end, so there is still a chance for him to stumble. But on Saturday, no one in the U.S. Open field looked steadier.

“A lot of fun,” Mickelson said, looking forward to the final round. “I can’t wait to get back out there playing.”

The final five holes take toll on leaders | 4:55 p.m.

Merion giveth. And Merion taketh away.

The much-scrutinized site of this year’s U.S. Open has -- as expected -- offered players a chance to improve their scores on a string of favorable holes around the turn. But it also serves up an unforgiving final stretch.

As Saturday afternoon turned to evening, one round after another turned chilly in the last five holes, player after player either losing their leads or falling away from the pack.

Hunter Mahan dropped out of first place with bogeys on Nos. 17 and 18, finishing at even par. Same thing happened to another one-time leader, Charl Schwartzel.

Rickie Fowler gave back strokes at Nos. 13 and 15, heading into Sunday at three over.

“There's some tricky pin placements out there every day and that's part of the reason why the scores are where they're at,” he said. “You can hit it on the green and there's some tough two putts out there."

How tough are the final five holes at Merion Golf Club?

As the last parings headed home, those holes were playing a combined 2.76 strokes over par. That ranks them as the toughest in the history of the U.S. Open.

Amateur Michael Kim, who went on a tear through the afternoon hours, dropped four strokes at the end to finish the third round at  four over.