The world's top-ranked player shot his best score of the week, an even-par 70, in the third round on Saturday at Chambers Bay, but he hardly sounded confident he could go much lower.
Asked whether he would be more aggressive Sunday, McIlroy, standing at four over, shrugged and said, "I don't know. I don't think I can. I've hit it as well as I can. And I've given myself plenty of chances. Just try to do the same thing and try to play the birdie holes better."
For the third straight round, McIlroy made only two birdies. He noted that he failed to birdie the drivable, par-four 12th hole and the 18th, which was playing as a par-five.
McIroy has not adapted to the fescue greens. He has needed more than 30 putts in each round, including 31 the past two days.
"It's been frustrating when you start to miss a few, and there's some that you don't quite know if you've made a bad stroke or if it's bobbled off line. You start to doubt yourself a little bit and doubt the greens. … I just haven't been able to get out of my way to let it go."
At 26, McIlroy has four major championship wins, and, unlike Phil Mickelson, one of those came in the U.S. Open in 2011 at Congressional.
"Came off the green on the last there and said to JP [Fitzgerald, his caddie], 'Thank God I've got one of these,'" McIlroy said of his 2011 win. "I'm glad my name is on the trophy at least once and I'll try to make it twice at some point."
Mickelson getting worse
One more Open. One more disappointing failed attempt for Mickelson. He shot his worst score of the tournament (77) to drop to 10 over. When the tournament is over, the five-time major winner will still be searching for a U.S. Open victory to complete the career Grand Slam. He is 0 for 25 in the national championship.
Mickelson, 45, shot 40 on the front nine and made only two birdies, giving him six for the week. His analysis of his troubles was brief and oddly cheery.
"As bad as my score was I hit a lot of good shots that ended up as bogeys," he said. "And through three rounds I haven't made a double."
He is correct. He has made only bogeys — 17 of them.
South African Louis Oosthuizen, the winner of the 2010 British Open at St. Andrews, fired in five birdies to shoot the best early score of the day, his second straight four-under 66.
Oosthuizen played the first two days with Tiger Woods and Rickie Fowler, who shot a combined 30 over. He opened with a 77 and was nine over through 20 holes, but he finished Saturday at one under and with a chance to make a run in the final round.
"It's going to be exciting from where I came back from," Oosthuizen said.
Tough to watch
The U.S. Golf Assn. sold 30,000 tickets to each round and because of the difficult terrain at Chambers Bay, it encouraged fans to use the 18,000 grandstand seats available. Of course, that still leaves many on the course trying to work their way through a maze of roads to get a decent sight line.
A family member of one player told a reporter that she gave up trying to wait for a grandstand seat because there was a line of dozens of people.
Among those struggling to see this week was Mickelson's wife, Amy, who has been a frequent follower of her husband at major tournaments.
"It's weird. Amy wants to come out and follow and she simply can't," Mickelson said after the first round. "I'll tell you, the golf spectators are probably the most dedicated fan. Any other sport you buy a ticket, you sit in a seat and you watch 100% of the action. In golf, you buy a ticket, you've got to walk miles in rough territory and you see but a fraction of the event. I give a lot of credit to the people who are out here."
Jamie Lovemark, the former NCAA champion from USC, shot a 75 and fell to two over for 54 holes.
Ben Martin, who began the day at three under, birdied his first hole but then fell apart. He wound up with an 86, making a triple bogey on No. 18