PINEHURST, N.C. (AP) -- There was something unusual in the opening round of the U.S. Open.
A bunch of scores in the 60s.
The best one of all was turned in by Martin Kaymer.
His confidence spurred by a win at The Players Championship, Kaymer birdied three of the last five holes Thursday for a 5-under 65, the lowest score from any of the three Opens played at Pinehurst No. 2.
The German got up and down for par at the 18th hole, rolling in a testy 6-foot putt to beat the 66 shot by Sweden's Peter Hedblom during the second round in 2005.
Graeme McDowell, Kevin Na and Brendon de Jonge were three shots back.
Kaymer beat a loaded field at The Players last month, snapping a stretch of 29 tournaments without a victory stretching over 18 months.
"I needed a win," Kaymer said. "Whether it was The Players or a regular PGA Tour event, I just needed it for my confidence, for all the hard work I've put in the last couple of years."
Ten other players were in the clubhouse at 69, meaning there were more under-par rounds in this opening round than the last two years combined.
At Merion a year ago, only five players broke par on Thursday.
At Olympic Club in 2012, there were just six scores in the 60s.
No one expected Pinehurst to stay this inviting through the weekend.
"There was some moisture on the greens and you were able to hold shots," Na said. "I was able to capitalize on a good tee time. But there's a long way to go. Obviously, I'm 2-under par right now, but at the end of the tournament even par is going to win this championship."
That's still a good bet.
The last two Open champions finished over par.
Phil Mickelson got off to a strong start as well in his bid for the career Grand Slam, attacking the course with deft iron shots on the way to a 70.
McDowell, who won the U.S. Open at Pebble Beach in 2010, was as steady as can be on this Donald Ross masterpiece, which has undergone a drastic makeover to restore its rustic look, with patches of natural vegetation - better known as weeds - taking the place of thick, lush rough.
The Northern Irishman bounced back from his only bogey at No. 4 with an eagle 3 at the par-five fifth hole. He added another birdie at the 14th and the rest of his card was filled in with pars, just the sort of solid, mistake-free golf that is required in the U.S. Open.
"You don't have to strike it amazing around here," McDowell said. "You just have to position the ball correctly at all times."
Na also made an eagle at No. 5 on the way to the best Open round of his career. He missed the cuts in 2010 and 2011, and finished 9 over at his last Open two years ago.
After thick cloud cover made things easier for the morning players, the blistering sun broke through and the temperature climbed to 90 by mid-afternoon. Still, there were low scores to be had, with 20-year-old Jordan Spieth, Dustin Johnson, Matt Kuchar and Henrik Stenson among the big group at 69.
Not everyone was thriving. The world's top-ranked player, Adam Scott, shot 73. Masters champion Bubba Watson sprayed shots all over the place on the way to a 76.
Spieth was in the thick of things again, making four birdies to put himself in contention at another major championship. He was tied for the lead heading to the final round of both the Masters and The Players Championship, but couldn't close out either on Sunday. It seems just a matter of time before the young Texan claims a career-defining triumph.
Maybe it will be at Pinehurst.
"I had a lot of fun today. You don't normally say that at the U.S. Open," Spieth said. "I was able to get into the flow early, and able to keep it going. One-under - I would take that four times."
Mickelson already has five majors, but this is the one he wants more than any other. Lefty has been the runner-up a record six times in this event, denying him the only big title missing from his resume. He has changed his grip to deal with a shaky putter, hoping that would help bring his first victory since capturing the British Open last July.
"This is a golf course where I get similar feeling to Augusta," Mickelson said. "You don't have to be perfect. You always have a chance. It is challenging. There are difficult shots. But they're manageable."
In recent weeks, Mickelson has been linked to an insider trading investigation. Clearly, he was able to stay focused on the course.
"I haven't done anything wrong," he said. "I'm willing to help out and would love to help out any way I can with the investigation."
Rory McIlroy, who won the 2011 U.S. Open in a rout at Congressional, opened with a 71.
Defending champion Justin Rose, who held off Mickelson a year ago at Merion, shot 72. There hasn't been a repeat winner in this championship since Curtis Strange in 1988-89.