Phil Mickelson was left to rue a missed opportunity despite making a solid start in his bid to win the US Open and complete the career grand slam at Chambers Bay.
Mickelson, who has finished runner-up a record six times, was among the early starters and took advantage of flat calm conditions to reach the turn in three under par.
However, the five-time major winner then carded three bogeys and one birdie on the back nine to card an opening 69 to finish one under par, four shots behind compatriot Dustin Johnson.
"I played well," Mickelson told Fox Sports. "I had a really nice round going and then made bogey on 13 and 14. I think the 13th is the hardest approach shot into the green. I did not leave myself the best shot and was way too far back and then made a good bogey on the next.
"(But) no complaints. I'm under par in the first round of the US Open and I am pretty pleased.
"I thought it was a very fair test. The set-up was good. I think everyone in the field is going to struggle with three to eight-foot putts when they are downhill because you can't hit it hard enough to hold the line and there is a lot of wiggle."
Mickelson had looked in trouble on the opening hole, missing the green to the left and seeing his ball roll down a steep slope onto the adjacent 18th fairway.
However, the 45-year-old - who celebrated his birthday on Tuesday - displayed his renowned short game skills by pitching to within inches of the hole to save par, in stark contrast to playing partner Bubba Watson who attempted to "putt" from a similar position with a fairway wood, failed to reach the putting surface and saw the ball roll back to his feet.
Mickelson birdied the third, fifth and eighth before dropping his first shot of the day by three-putting the 10th from long range following a poor approach from a fairway bunker, but bounced straight back with a birdie from 12 feet on the next.
After surprisingly opting to lay up on the short par-four 12th rather than attempt to drive the green, Mickelson had to settle for par there and then bogeyed the 13th and 14th after finding sand on both holes.
Johnson had started his round on the back nine and carded birdies at the 11th and 12th before picking up further shots on the first, fourth, fifth and seventh.
The 30-year-old ruled himself out of the Ryder Cup last year by taking a lengthy break from the game to deal with "personal challenges", prompting allegations in the United States of a positive test for cocaine - claims which have dogged him for several years but which he has always strenuously denied.
Johnson again dismissed the drug claims in his first interviews since the announcement earlier this year, revealing his battle had been with alcohol, and overturned a five-shot deficit in the final round to win the WGC-Cadillac Championship in March.
At six under par, Johnson was two shots ahead of Sweden's Henrik Stenson, who had carded three birdies in a row from the 14th, with Ryder Cup rival Patrick Reed also four under with three to play.
World number one Rory McIlroy was struggling on the greens as he stood one over with two to play, but former Ryder Cup captain Colin Montgomerie was one under after 16 holes in his first US Open appearance since 2008.