Dustin Johnson was satisfied despite rueing missed opportunities during his first round at the US PGA Championship on Thursday.

The American fired a one-under 69 at Bethpage Black to be six shots behind leader Brooks Koepka in New York.

Johnson was happy with how he played, but he knows he could have scored better.

"I hit it really well," the world number one told TNT after his round.

"I drove it good, hit a lot of greens, gave myself a lot of opportunities, I felt like I hit a lot of good putts that a few of them could have gone in that didn't.

"But I'm very happy with the way I played and the opportunities I gave myself."

Johnson made two birdies and one bogey in his round. The lone bogey came on the first hole and he kept a clean card from there on out.

He said he can definitely play better, but he was happy to be at least in shouting distance of Koepka.

"I drove it very well so I was very pleased with the driving," Johnson said. "You know, make a few more putts, that's about it, but you can always make more putts.

"I like the way I swung the golf club and I thought I controlled the golf ball very well and you know, it's just a hard golf course, it's hard to get it close to the hole and a lot of these holes it's hard to hit the fairway.

"So I just need to do a little bit more of that tomorrow, hit it in the fairway and just give myself more opportunities."