Updated June 15, 10:15 a.m.
ARDMORE, Pa. -- Following a 3-under-par 67 on Friday, Billy Horschel finished Friday in the lead at the U.S. Open, tied with Phil Mickelson.
The second round, delayed three hours thanks to the completion of Thursday's first round, was completed shortly after 10 a.m. Saturday morning, when 23 of 26 groups who teed off in the afternoon on Friday finally made their way in.
Saturday's third round is scheduled to begin at 12:28 p.m. Players will go off in threesomes on both holes No. 1 and 11.
Mickelson and Horschel lead by one shot over five players at even-par, including Luke Donald, Steve Stricker, Justin Rose, Ian Poulter and amateur Cheng-Tsung Pan.
Horschel's 67 came after he was forced to finish his first round in the morning before heading back out for his second round not even an hour later. His round tied Mickelson's from Thursday for the low score of the tournament.
"Yeah, 66 sounded better but I three-putted No. 13," he said. "I'll take the round. It was a good day. Obviously, it was a long day [with] 29 holes.
"But it was a great day. Four birdies at a U.S. Open. I'll take it."
Mickelson, who at one point fell all the way back to even par, birdied the 18th hole after the horn had sounded to shoot a 2-over-par 72 and reclaim a share of the lead.
"It was a nice way to finish on the 18th," Mickelson said. "I fought hard all day, let a lot of birdie opportunities slide early and in the middle of the round. I fought hard to stay in there and hit a lot of good quality shots. Made a bunch of good pars.
"On 18, when you don't really expect to get one, I put the ball in a good spot and was able to roll one in. It felt good."
Twelve players are within at least three shots of Mickelson and Horschel.
World Nos. 1 and 2 Tiger Woods and Rory McIlroy both finished Friday 3-over for the tournament. They'll be paired together for the third straight day on Saturday.
After his grimacing and shaking of his left arm caught attention on Thursday, Woods disclosed Friday afternoon that he's been dealing with an elbow injury since he won the Players Championship back in May (see story). Woods was another who had to finish his first round Friday morning only to head back out onto the course shortly thereafter.
"Long day," he said, laughing. "And I'm hungry."
Seventy-three players survived the 8-over-par 148 cut line to play the weekend. Notable names who made the cut right on the number include Dustin Johnson, Brandt Snedker and Mike Weir.
Other notables who will miss the weekend include Zach Johnson (11-over), Keegan Bradley (12-over), Nick Watney (11-over), 2010 champ Graeme McDowell (13-over), 2009 champ Lucas Glover (13-over), Angel Cabrera (15-over), and 2003 champ Jim Furyk (16-over).
Scores ballooned for a second day at Merion on Friday, when despite soft conditions, the rough proved too much for many too handle (see story). Just one hole, the par-3 13th played under par on Friday.
Louis Oosthuizen withdrew from the tournament on Friday with an undisclosed injury. Oosthuizen nearly didn't come to Merion this week, as his wife is pregnant with their third child. The 2010 British Open champion put up a 75 in his opening round.
Robert Garrigus (16-over) also withdrew Saturday morning.
'That Kangaroo stole my ball'
Mickelson's round was brought to temporary stop on the front nine when a groundhog ran onto the fairway. Watch the video here.