Phil Mickelson rolled in an 18-foot birdie putt in fading light at the 18th hole to grab a share of the lead in Friday's second round of the US Open when play was suspended due to approaching darkness.
The putt gave Mickelson a round of two-over-par 72 for a total of one-under 139 and tied him with fellow-American Billy Horschel, who fired a dazzling three-under 67 on a brutally difficult day at the weather-delayed championship.
The pair were perched atop a jam-packed leaderboard that had five players one shot back and another five golfers one more stroke adrift, with tournament favorites Tiger Woods and Rory McIlroy well within striking distance at three-over par 143.
Mickelson, the clubhouse leader after shooting an opening round 67 before lengthy weather delays suspended Thursday's first-round play, held the lead for much of Friday before back-to-back bogeys from the 12th.
"I wasn't expecting birdie there. It's a very difficult hole," said the left-hander, who had three-putted the 12th and failed to get up-and-down after half-plugging his ball in the greenside bunker at the short par-three 13th.
His 18th hole birdie was his first of the day.
"I got shut out today," he said, exasperated at not taking advantage of other birdie chances. "I played really well.
"I didn't feel the score was what I thought it should be."
The 26-year-old Horschel, who followed up three successive top 10s on the PGA Tour with a victory in April at the Zurich Classic had four birdies and a lone three-putt bogey.
"It was a great day. Four birdies at a U.S. Open, I'll take it. I wish I had a couple more, though," he said.
Bunched at level par, were former world number one Luke Donald (72), his fellow Englishmen Justin Rose (69) and Ian Poulter (14 holes), American Steve Stricker (69) and amateur Pan Cheng-tsung of Taiwan (nine holes).
Tied at one over par were Nicolas Colsaerts of Belgium, who shot 72, Australian John Senden (71), Jerry Kelly (through 12), Charley Hoffman (13), and 19-year-old amateur Michael Kim (11).
Sunshine on Friday replaced the rain that had plagued the tournament, the wind kicked up and players struggled to make par as Merion Golf Club showed it was still a master test for the world's best golfers.
Merion's tilted fairways fed balls into the rough and tricky pin positions coaxed players into a slew of three-putt bogeys.
Woods battled through the course challenges and an injured left arm to finish a 73 in the morning, then shoot an admirable 70 in the afternoon to reach the halfway stage at three-over.
"It's hard with the wind and the pin locations. They're really tough," said Woods, who was tight-lipped about his injury.
"It's hard with the wind and the pin locations. They're really tough," - Tiger Woods.
"A lot of guys are missing putts and blowing them by the holes."
Sixty-eight golfers had not yet finished their rounds and were returning Saturday morning at 7:15 a.m. (1115 GMT) to the classic layout in the Philadelphia suburbs.
Donald began the day leading clubhouse leader Mickelson by a stroke, standing four under par with five holes still to finish.
But the world number six bogeyed two of the last three holes in tough scoring conditions to give the American a one-shot lead when the weather-delayed first round was completed.
Donald briefly reclaimed the lead with a pair of early back-to-back birdies in his second round but tumbled back down with a late stretch of five bogeys in six holes including four in a row.
"U.S. Opens get harder as the week goes on," said Donald, who is looking to break through for his first major title.
"I'm excited to be in contention, and have a chance."
The projected cut to reduce the field to the top 60 and ties was estimated to come at seven over par 147 after second-round play on Friday had players averaging nearly five over par.
Among high-profile competitors who will not qualify for weekend play were a trio of former U.S. Open champions in Angel Cabrera of Argentina, who shot an 81 for 155, American Jim Furyk (79/156) and Northern Ireland's Graeme McDowell (77/153).
"It's that hard, it's that difficult," said McDowell, the 2010 champion and runner-up last year.
"I'm disappointed, of course. It's not the way I wanted to play the last couple of days. But this place is very hard."