US Open leader Phil Mickelson began his second round Friday facing a malevolent course at Merion that already tested the talents of such rivals as Tiger Woods, Adam Scott and Luke Donald.
Merion's dense rough and firm greens mixed with brisk winds to punish every errant shot, the 6,996-yard layout ending any notions it might be vulnerable due to recent heavy rains or its relatively small length.
Instead, Merion inflicted mayhem on the field of 156, frustrating some and shattering others as players faced up to 32 holes on Friday due to storms that wiped out more than four hours of play on Thursday.
We are all struggling because it's such a penalising golf course. It's a course that's withstood the test of time and it's challenging the best players in the world
"We are all struggling because it's such a penalising golf course," Mickelson said after round one. "It's a course that's withstood the test of time and it's challenging the best players in the world."
As heavy rains dried up, quaint and quirky Merion turned from maid into a monster of Dr. Jekyll and Mr. Hyde proportions.
"As the week wears on and the conditions get a little bit dryer, a little bit firmer, I think the course is going to get even more difficult and the scores are going to hover very close to par," Mickelson had predicted.
England's Donald was the low man in the clubhouse, his two-over par 72 in round two following the finish of a 68 in the morning putting the former world number one on level par 140.
"You try not to panic in US Opens. You just take it as it comes," Donald said. "You are going to make mistakes. I've got to minimise those mistakes over the next two days."
A second-round 71 by Aussie John Senden put him on 141. He credited the deep rough for the brutal scores.
"It's because of the difficulty when you miss," Senden said. "The rough is so long here. It's just demanding. If you miss, you are really scrambling. It demands all parts of your game being great."
American Billy Horschel, who won his first PGA title in April at New Orleans, was two-under for the round with four holes to play in only his second major. As a teen, he missed the cut in the 2006 US Open.
Donald shared the lead with Mickelson early in the second round, dropping a 30-foot birdie putt at his second hole, the par-4 12th, and following with a chip-in from a greenside bunker at the par-3 13th.
Donald, seeking his first major title, looked on form to improve upon his best US Open finish, a share of 12th in 2006 at the only major where he has never cracked the top 10.
But Merion would take revenge. Donald took a bogey at the 15th and another at the par-5 second. He birdied the par-3 third, but then made four bogeys in a row starting at the fourth, where his bid to chip over a bunker put him in it and he needed an eight-foot putt to save bogey.
"The pins were a lot more tucked. They were difficult to get to," Donald said. "I didn't play the par-5s well. The other bogeys I didn't feel I made too many mistakes. It's just a tough golf course."
World number one Woods, a 14-time major champion seeking his first major title since the 2008 US Open, finished 36 holes on 143 after a second-round 70.
Woods, who admitted feeling pain in his left wrist after blasting out of dense rough in Thursday's first round, seeks a record-tying fourth US Open triumph but has never won when over-par for 36 holes.
Starting on the back side, Woods birdied the par-3 13th only to stumble with bogeys at 14 and 18. Birdies at the par-5 second and fourth lifted him but he botched a greenside chip to bogey the par-4 seventh.
Playing alongside Woods in the feature group, world number two Rory McIlroy also fired a 70 to join Woods on 143 while third-ranked Australian Scott, the reigning Masters champion, stumbled to a 76 and was likely to miss the cut.
McIlroy opened with back-to-back birdies at 11 and 12, made bogeys at 14 and the first, then followed a birdie at the third and a bogey at the fourth. A birdie at the eighth was followed by a bogey at the ninth.
Scott began a run of four bogeys in a row at the par-3 third and had seven in all.
Only five players broke par in the first round that was completed Friday, leaving late starters like Mickelson and Belgium's Nicolas Colsaerts, who opened with a 69, with no hope of finishing the second round until Saturday.