(CNN) -- Dealing with Merion is turning out to be tough enough. But Tiger Woods is also battling an injury at the U.S. Open in Pennsylvania.
Woods revealed that he hurt his left arm while winning The Players Championship last month, which would explain why he grimaced noticeably on several occasions in the first round.
The world's top-ranked golfer was back in action in the second round Friday and shot a level-par 70 to complete two rounds at three-over-par 143.
Asked to provide more details about injury, Woods didn't elaborate.
"Well, it is what it is," Woods said.
Woods is bidding to win his 15th major but first since 2008 at the U.S. Open at Torrey Pines.
Back then he had to deal with seemingly a more serious injury -- a broken leg. He memorably beat Rocco Mediate in a playoff.
Given the challenging conditions at Merion, Woods suggested his total might not be so bad heading into the final two rounds.
Storms caused delays of more than four hours Thursday -- Woods had to complete his first round Friday -- and play was eventually suspended due to darkness. Windy conditions added to the degree of difficulty at Merion's shorter East Course.
Woods, Rory McIlroy and Masters winner Adam Scott made for a dream pairing and while Scott struggled, Woods and McIlroy -- the second-ranked golfer -- fared better.
Seen chatting amicably during the round, the duo compiled identical scores in the first two rounds.
Beginning at the 11th hole, Woods birdied the 13th for a good start. Two bogeys, however, on the 14th and 18th, meant he had work to do on the first nine.
He hit birdies on the second and fourth, although with a one-under-par in sight, he bogeyed the seventh. Americans Billy Horschel and Phil Mickelson, a five-time U.S. Open runner-up, co-led through two rounds with a one-under-par 139.
"I played well," Woods said. "I just made a couple of mistakes out there.
"But I really played well. Maybe I could have gotten one or two more out of it, but it was a pretty good day."
McIlroy, who hasn't hit peak form in 2013, hit four birdies and four bogeys.
"I got through that tough stretch from 14 to 18 in only one over which was a pretty good effort," he told Sky Sports. "I played solid. It felt like every time I made a birdie I made a bogey straight away.
"It's a course where you sort of feel like you can shoot a score but where they put the pins ... it's just tricky and tough. I'm right there for the weekend and I'm happy about that."
Scott bettered Woods and McIlroy in the first round, shooting a 72. But he came undone nearing the end of his second round, hitting four bogeys in a row from the third to the sixth hole.
"I just lost my rhythm early this morning when it was a bit cold and windy and just fought with it all day long," Scott said. "The putter kind of cooled off.
"I would have liked to make some putts and then you're always happy."