Two-time defending U.S. Open champion Brooks Koepka said he has "a lot of confidence" after making a solid start at Pebble Beach.

Koepka – seeking a third successive U.S. Open crown – carded a two-under-par 69 to be four shots behind leader Justin Rose on Thursday.

Not since Willie Anderson in the early 1900s has a player won the major tournament three years in a row, but Koepka – who is coming off back-to-back US PGA Championship titles – is oozing confidence.

When asked if he was even calmer with every passing major, world number one Koepka told reporters: "You definitely get more comfortable.

"And I have a lot of confidence, there's no doubt of that. It's becoming easier and easier as I keep playing them."

American star Koepka made a hot start in his bid for a three-peat, birdieing four of his opening six holes in the first round.

Koepka dropped a shot at the eighth hole but bounced back by birdieing the 12th, though he bogeyed the 13th and 17th to close out the day.

"It's a battle if you're not going to hit fairways. If you're not going to hit greens, it's going to be tough," the 29-year-old said. "I'm actually quite pleased.

"I don't know how many fairways I hit from eight on in. I didn't hit many. And didn't hit many greens. The up-and-down I made on 16, had a good chance on 15, but sometimes those greens are so slopey, and you've got a four-footer and you're playing it with what feels like two feet of break. It's going to happen."

Koepka added: "You know what you're going to get at Pebble. I think it's going to be a lot of rough around the greens, around the fairway. So if you miss it you can be in trouble. The putting surfaces are as good as I've seen them.

"Probably the best poa I've putted on. And they might firm up as the week goes on, I'm assuming they will. And even if they do it's not like they're overly firm right now, especially with the fog and mist coming in in the morning. I think it's going to be just fine."