Britain's Nick Dougherty, taking advantage of rain-softened conditions with a precise short game, fired a two-under-par 68 to forge one shot clear in the US Open first round.
While world number one Tiger Woods battled to a 71 at Oakmont Country Club, one of golf's toughest layouts, Dougherty carded four birdies and two bogeys in his lowest score at a major championship.
Dougherty, who won his only European Tour title at the 2005 Singapore Masters, birdied three of the last eight holes to end his round one ahead of big-hitting Argentine Angel Cabrera.
Twice US Masters champion Jose Maria Olazabal, who came close to an ace at the par-three sixth, and American Bubba Watson, making only his second appearance in the tournament, were next best on 70.
Woods, third-ranked Jim Furyk, defending champion Geoff Ogilvy of Australia and Fiji's Vijay Singh were among a group of 16 bunched on 71.
Woods, bidding for his 13th major victory, made a stumbling start after finding a fairway bunker off the first tee but was delighted with his par-birdie-par finish.
Padraig Harrington and Graeme McDowell are both well placed after carding similar rounds of three-over 73.
Ernie Els, US Open champion at Oakmont in 1994, also opened with a 73 and three-times major winner Phil Mickelson, who has been nursing a wrist injury for the last two weeks, carded a 74.
Only two players in the 156-strong field returned sub-par scores on a day of typical US Open grinding when the average was 75.32.
American David Toms, who ended up with a 72, got to three under after 12 holes and Briton Justin Rose (71) was two under after 13 before both fell back over the punishing five-hole stretch starting at the par-four fifth.
Several big names effectively shot themselves out of contention, twice champion Retief Goosen double-bogeying the last for a 76 and world number six Henrik Stenson and Spaniard Sergio Garcia limping to 79s.
