Mickelson shot a second-round 2-over 72 and finished the day tied with Billy Horschel for the tournament lead. Sixty-eight golfers remained on the course and will finish their second rounds Saturday morning.
"I struggled with a lot of short putts today and I've been putting really well," Mickelson said. "So hopefully tomorrow, today will just be an anomaly on the greens. . . . Today should not have been an over-par round as well as I played."
Tee to green, Mickelson was very good. His ball-striking was slightly off in the early going, but he ended up hitting 10 of 14 fairways and 13 of 18 greens in regulation. He was 11 of 14 and 14 of 18 on Thursday.
But he was a hair off on a number of putts and 3-putted the 12th when a three-footer lipped out.
"Quite honestly, after we had had two waves of players go through, the greens weren't anywhere near like they were when I played yesterday morning. They were just pristine," Mickelson said. "And with the field being cut in half, I expect them to be every bit as pure."
Mickelson had 33 putts on Friday, a day after he needed only 29. It could have been worse had he not drained a 20-foot attempt on the final hole. The par-4 18th played as the second-hardest hole on Friday, only behind the par-3 9th.
"At 18, I was fortunate to get one," Mickelson said. "I put the ball in a good spot where I had an uphill, aggressive putt at it, and I was able to roll it in."
Mickelson and the 26-year-old Horschel will be partnered for the final pairing of the third round. Mickelson, a five-time runner-up in the U.S. Open, has been in this position plenty of times before. He was last in contention at the 2010 Open at Pebble Beach.
"There are a lot of players that are right there around par, a couple over," Mickelson said. "I think this golf course presents the chance to shoot a low round, although not many players have done it."
As well as Mickelson played, he was not the best ball-striker in his group. Steve Stricker didn't show many cracks during a round that ended with a 69. He stood in a five-way tie for third place at even-par.
When their threesome, which also included Keegan Bradley, teed off at 3:41 p.m. there was a chance they would not finish before play was suspended. But when play was called at 8:27 p.m. they were on the 18th green and elected to finish up.
Mickelson's round got off to a shaky start. He drove into the bunker on 1 and then 3-putted for a bogey. He sliced his drive on two and hit his second into a fairway bunker, but recovered with a splendid third shot to eight feet. He 2-putted for par.
The 42-year old got up and down at No. 5 after he drove into the hazard. But Mickelson missed birdie putts on five of the next six holes. He almost holed out from the eighth fairway, but missed the resulting four-foot putt.
He had a fried-egg lie in the back bunker on 13 and took a bogey. But Mickelson rallied on the home stretch to stay atop the leader board. Two days ago, some were questioning his decision to fly back to California on Tuesday to attend his daughter's graduation.
Now he's back in the lead.
"I just like being in the mix," Mickelson said. "The way I'm striking the ball, the way I have control off the tee, and as good as the putter feels, although I didn't show it today, I'm very excited about the opportunity this weekend."
Contact Jeff McLane at email@example.com. Follow on Twitter @Jeff_McLane.