By Mark Lamport-Stokes

OAKMONT, Pennsylvania (Reuters) - Having paid a steep price for wayward approach shots in the opening round at Oakmont Country Club, world number one Jason Day clawed his way back into contention at the weather-hit U.S. Open on Saturday.

The Australian parred his last three holes to end a marathon second round that began early on Friday with a one-under-par 69, a five-over total of 145 leaving him nine strokes off the early lead in the year's second major championship.

With conditions expected to become more difficult over the weekend as the notoriously tough golf course firms up under relentless sunshine, Day has set his sights on getting to back to level par.

"It was good to come back out this morning and par the last few holes, which are very difficult to do because seven, eight and nine are not easy," Day told reporters. "The greens are only going to get firmer and faster, and same with the fairways.

"I'm trying to claw my way back to even par. I think, if I can get back to even par, that I may have a good chance at giving myself a shot at winning. But obviously, there's plenty of golf to be played."

Day has been the game's hottest player over the past 12 months with seven tournament wins, including last year's PGA Championship at Whistling Straits, but left himself with plenty of work to do after struggling in the opening round at Oakmont.

"The first round, obviously, was terrible," the 28-year-old Queenslander said. "I gave myself plenty of opportunities in the first round.

"I felt like I drove it pretty good in the first round and then missed too many greens, especially with short clubs, and a couple three-putts in there as well."

Day readily accepts that he faces an uphill task in pursuit of his second major victory, with long-hitting American Dustin Johnson dropping just one shot over the first 36 holes to set the tournament pace.

"Dustin Johnson is playing some pretty good golf right now," said Day. "It definitely suits his game because he can take some lines here that a lot of other guys can't and lay it back when he needs to.

"He's going to be tough to beat, especially with how he's playing. But 36 more holes. There's so much golf to be played, and I've got to be patient."

(Editing by Larry Fine)