Rory McIlroy conceded runaway leader Brooks Koepka was playing golf on a "different level" as his major drought continued in the US PGA Championship.

McIlroy's second US PGA title at Valhalla in 2014 remains his last to date and the 30-year-old was never in contention at Bethpage after opening rounds of 72 and 71 on Long Island.

In stark contrast Koepka is seeking his fourth major victory in his last eight starts and followed a course record of 63 with a 65 for a halfway total of 128, the lowest in major history by two shots, to claim a tournament-record seven-stroke lead.

It was a lead few people expected Koepka to relinquish and although he missed a short birdie putt on the first after a 337-yard drive, the 29-year-old American birdied the second and fifth before surprisingly missing from two feet for par on the ninth.

At 13 under par Koepka still enjoyed a seven-shot lead over world number one Dustin Johnson and Thailand's Jazz Janewattananond, with England's Matt Wallace, Harold Varner and Luke List two shots further back.

McIlroy, who had looked set for an early exit after dropping five shots in his first three holes on Friday to slump to seven over par, played his last six holes in four under to make the cut with a shot to spare.

The upward momentum continued on Saturday with a front nine of 32, but McIlroy eventually had to settle for a 69 to finish two over par and was left to join the chorus of approval for Koepka's performance.

"It's awesome. It's so good," McIlroy said. "It's great to watch and I watched most of it yesterday afternoon.

"He's definitely, in these events, playing on a different level than most anyone else. It will be fun this afternoon to see if he goes out there and just keeps his foot down and extends that lead.

"It's firming up a little bit but I still think it's pretty scoreable. If Brooks hits it the way he's hit it the first couple of days I can see him shooting a good score in the 60s and if he does that obviously it's going to be very hard to get near him."

McIlroy missed good chances for birdie on the first three holes, but made amends by holing from 30 feet for an eagle on the par-five fourth before coming up inches short of a hole-in-one on the eighth following a brilliant five-iron approach from 224 yards.

However, the Northern Irishman was then unable to get up and down from a greenside bunker on the difficult 10th and three-putted the 14th, where his par putt caught the edge of the hole and spun out.

"It definitely could have been better, it's the best I hit it all week for sure," McIlroy added. "I sort of got it going on the front nine there, (hit) a couple of loose shots on the back nine but I played well. I didn't convert as many chances as I would have liked but it was an improvement on the last couple of days.

"I hit the ball as good as I've hit it in a while, gave myself plenty of chances. If I had made a couple of putts I could definitely have shot 65, 66 easily out there today.

"If you look at the last nine I played yesterday and the first nine today I was seven under par for those 18 holes so it's just about putting it all together on the right day.

"I definitely felt like I left four or five out there, but you have to put it all together to shoot a really good score. I was close to doing that today but just not quite."

The best scores of the day so far had come from Ireland's Shane Lowry and Thailand's Kiradech Aphibarnrat, who both shot 68 to improve to two over.

But conditions were far from easy and 2002 champion Rich Beem, who covered the back nine in 30 on Friday to make the cut, played the same stretch in 43 on Saturday in an 82.

Lowry, who followed an opening 75 with a 69 on Friday to make the cut, said: "Playing golf on the cut mark is quite difficult sometimes. I was able to go out and play a bit freer today and kind of let it go a little bit.

"I drove it well the last couple of days and I feel like I missed a couple of chances coming in as well. But anything under par around here is good.

"I don't know what happened the first day. I think it might be an element of paying the golf course a little bit too much respect."