US Open Update: Tiger Woods admitted he is struggling with his knee after shooting a first-round 72 at Torrey Pines.

The world number one was returning to action after knee surgery and a two-month lay-off and at times was grimacing in pain after his drives.

That was particularly evident after his tee shot at 18, which split the fairway on the par five which was ruined by a three-putt par.

Woods said afterwards: "The knee is a bit sore right now. That wasn't the only one that I winced on. It is what it is, you've got to deal with it and continue playing. Unfortunately I three-putted the last and there is no excuse for that."

Woods' return to competitive action began with a double-bogey six and he did well to recover to be out in one-under 35.

"I had a terrible start," he added. "I couldn't ask for a worse start. It's not like I haven't been there before. I've made bogeys before, just not two of them on the first hole. Stay patient, there are some birdie holes out there. I got back to under par, unfortunately I didn't stay there."

Nationwide Tour player Justin Hicks took the early lead with his opening 68. He admitted he had tried to treat his second US Open appearance just like a practice round.

The 34-year-old from Michigan finished 80th on the Nationwide Tour last year but was a surprise leader on day one at Torrey Pines.

"It is not every day you get to say you shot under par at a US Open so it feels pretty darn good," said the American. "I had a pretty good idea out there that things were going well, making as many birdies as I did.

"There were certainly times when I could feel more nervous energy but I did my best to reinforce the positive thoughts in my head. I've got my best friend out here this week caddying for me and we just did our best to feel it was a practice round, just another day on the golf course having fun with it.

"Today I had this mindset - the fact is that when you get it going you just have to ride it out as best you can."

Chris Devlin was having a torrid time and was 12-over with three holes to play on his US Open debut. He and Pádraig Harrington are the only Irishmen in the field.

The British Open champion was due to get his round under way alongside defending champion Angel Cabrera and Davis Love III.