Adam Scott went from one off the lead to eight shots off the pace after a marathon second day at the US Open, while John Senden is just two off the lead and tied eighth at Merion Golf Club.
Masters champion Scott restarted his rain-interrupted first round at three-under par through 11 holes but was 10 over through the next 25 holes as he completed round one and pushed on through round two.
It left the Queenslander at seven-over par thanks to rounds of 72 and 75, eight shots adrift of American leaders Phil Mickelson and Billy Horschel, the only men under par at one under.
Horschel, a recent winner on the US PGA Tour but nonetheless still a relatively unheralded 26-year-old, produced an impressive three-under 67 in extremely tough conditions.
Mickelson drained a 20-foot birdie putt on the last hole to shoot a 72 and join his countryman on top, one clear of five others.
Englishmen Luke Donald (72), Justin Rose (69) and Ian Poulter (14 holes), American Steve Stricker (69) plus Taiwan’s 21-year-old amateur Cheng-Tsung Pan (nine holes) all sit at even par in the uncompleted second round.
Trying to make up for lost time from Thursday, play was extended until darkness, but 68 players were left to complete their second rounds.
Tiger Woods and Rory McIlroy shot 73 in the morning round but backed it up with matching 70s to be three over and well in contention, tied for 17th.
Senden managed four birdies, including a memorable long curling putt from off the green on the difficult fifth hole, but added three bogeys and a double bogey for a 71 in the second round.
But for Scott it was nothing but grief with nine bogeys, a double bogey and just one birdie in the 25 holes he played.
“I got off on the wrong foot and just struggled to find my rhythm all day,” Scott said.
“I didn’t make the putts I needed to kind of save some shots here and there and they just slipped away too easily.”
The 32-year-old sits right on the projected cut number.
Mat Goggin backed up a great 68 in the morning with a 74 to be two-over par and tied 13th.
Jason Day was three-over par for his round and the championship through 14 holes to remain in contention, while 2006 champion Geoff Ogilvy ground hard for a 70 to remain four over following his morning 74.
Alistair Presnell will be sweating the cut line after finishing at eight over, the same score Aaron Baddeley sits on through 13 holes, but the US Open will be over for Marcus Fraser (+12) and Marc Leishman (+13).