Rory McIlroy felt an even-par 70 in the US PGA Championship first round was not too bad after battling in San Francisco.

The four-time major champion struggled to a 70 that included four birdies and four bogeys at TPC Harding Park on Thursday.

McIlroy said it was a missed opportunity in the first round, but also believed his score could have been worse.

"Condition-wise, the wind wasn't up and it was a little warmer, so that was nice," the Northern Irishman said.

"I felt like the course was there for the taking. Jason Day shot five under. There's been a few four unders.

"The pins were tucked a little bit. The greens are getting a touch firmer. A lot of wind directions. For example, there's a few holes where the wind was – or the pin was on the right side of the green and the wind blowing right to left, so it's hard to get yourself to get close to those. You're sort of hitting to the middle of the greens a lot.

"It was there for the taking today. I mean, I feel like I definitely could have been a few shots lower, but you know, I sort of grinded it out and with how I hit it on the back nine, even par actually wasn't too bad."

After a birdie at his opening hole – the 10th – McIlroy made three consecutive bogeys starting at 12 before recovering.

McIlroy said he needed improvement in the second round, having struggled off the tee during his opening 18 holes.

"Actually got off a nice start, birdieing the first hole of the day, the 10th hole for us, and then, yeah, I made three bogeys in a row. Ended up being a pretty good bogey on 14," he said.

"And then after that, was happy, I birdied three holes in a four-hole stretch to get back to under par for the day which was nice. That was good.

"Then on our second nine, the front nine, I didn't hit fairways, and then from there, the way that the pins were tucked, I was just trying to play to the front of the greens and two-putt from 40 feet and move on to the next hole.

"Need to hit a few more fairways tomorrow to try to attack some pins and get it closer, and not leave myself four- and five-footers for par all day."