ARDMORE, Pa. -- The frustration was visible on Phil Mickelson's face Saturday in the third round of the U.S. Open.
If his birdie attempts weren't burning the edge of the hole, they were going in a different direction than what Mickelson had expected, a trait of the befuddling greens on Merion Golf Club's East Course.
But Mickelson never allowed himself to become distracted by the near-misses and finally broke through on the back nine with three birdies that gave him a real chance to win his very first national championship on Sunday, his 43rd birthday.
Mickelson shot an even-par 70 for a 54-hole score of 1-under 209, the only player to finish three rounds under par. He held a one-stroke lead over Hunter Mahan, Steve Stricker and Charl Schwartzel and was up by two shots over Justin Rose, Luke Donald and Billy Horschel, who shared the 36-hole lead with Mickelson.
The third round likely marked the end of Tiger Woods' bid to end a drought in majors that extends back five years. Woods shot a 76 and goes into the final round looking at a 10-stroke deficit.
A four-time major champion, Mickelson has been in this position before but has fallen short, finishing as the Open runner-up a record five times.
However, this is the first time he has held sole possession of the lead entering the final round (he was co-leader at Winged Foot with Kenneth Ferrie in 2006).
"I don't think I feel any more pressure than anybody else who wants to win the tournament, a major championship, the U.S. Open," he said. "But it would certainly mean a lot to me. This is a tournament for years I've had opportunities, I've come close. It would mean a lot (Sunday) if I could play some of my best golf, certainly if I can play the way I have been."
Mickelson showed the patience of a veteran Saturday, especially on the front nine where the birdie putts weren't dropping.
He was 2 over for the day at the turn and trailed by three strokes.
But the round turned at the 10th and 11th holes where he sank birdie putts of 4 and 15 feet.
He topped it off with a 10-footer for a birdie 2 at the 254-yard 17th hole.
Even though he finished with a bogey at the brutal 18th, he still had a one-stroke lead and plenty of optimism.
"I love being in the thick of it," he said. "I've had opportunities in years past and it has been so fun, even though it's been heartbreaking to come so close a number of times and let it slide. But I feel better equipped than I have ever felt heading into the final round of a U.S. Open."
Only nine players were within five shots of Mickelson entering the final round. Other than Mickelson, the other challengers have combined for one major -- Schwartzel's win in the 2011 Masters.
Schwartzel gained the lead with a birdie at No. 10 and was joined in first by Donald and, later, Mahan.
But Schwartzel and Mahan bogeyed their last two holes and Donald finished up bogey-double bogey. Still, Schwartzel and Mahan broke par with 69s, and Donald had a 71.
"Whenever you shoot under par on Saturday at the U.S. Open, you can't be too disappointed," Schwartzel said. "Anything under par is fantastic here."
That will be the goal on Sunday for everyone, particularly those in the top 10. Stricker, at 46 and 0-for-58 in majors, will join Mickelson in receiving sentimental support.
Then you have the 20-somethings -- Schwartzel (28), Horschel (26), Jason Day (25) and Rickie Fowler (24), who moved 28 spots up in the standings with a 67, the best round of the day.
But all eyes will be on Mickelson. He welcomes the opportunity.
"It's got the makings to be something special," he said, "but I still have to go out and perform."
Woods needed 36 putts on the severely undulating greens. He blamed his inability to gauge the speed of those baffling putting surfaces for his three days of uneven play.
"It's certainly frustrating because I was feeling like I was playing well this week, and I just didn't make the putts I needed to make," he said.
This Open marks exactly five years since Woods won his last major, at Torrey Pines. His pursuit of Jack Nicklaus' career record of 18 majors remains stalled at 14.
"I only hit one bad shot and made 10," he said in his classic no-fault mode. "My first shot was into the wind. My second one, I thought it was even better, and it went out of bounds by five inches. And then the third one wasn't great."
MCT Information Services contributed to this report.