World number one Dustin Johnson ensured the final round of the US PGA Championship was not the procession many had feared as he battled to catch runaway leader Brooks Koepka.

Koepka had followed a course record of 63 on Thursday with a second round of 65 to set the lowest halfway total in major championship history and took a seven-shot lead over Johnson, Harold Varner, Luke List and Jazz Janewattananond into the last day at a blustery Bethpage.

The 29-year-old American is 67 under par in majors since the start of the 2016 US PGA, 26 shots better than any other player during that span, and is seeking a remarkable fourth major victory in his last eight starts.

With the US PGA moving from August to May this year, Koepka can also become the first player to hold back-to-back titles in two majors at the same time following his US Open wins in 2017 and 2018.

However, Johnson, who would lose top spot in the rankings to Koepka if his good friend retained his title, had other ideas and birdies on the fourth, sixth and ninth completed a flawless front nine of 32.

Koepka had made a poor start with a bogey on the first but reduced the par-five fourth to a drive and an eight-iron to set up a two-putt birdie and get back to 12 under.

The best score from the early starters was a pair of 68s from Americans Beau Hossler and Gary Woodland, with Northern Ireland's Graeme McDowell having to settle for a 70 after covering the front nine in 33.

"My game feels good, it really does," said McDowell, who will return to the scene of his 2010 US Open triumph next month when the championship returns to Pebble Beach. "I'm trying not to get too destroyed by this golf course.

"This is not a golf course that I would pick for me in a major championship and Pebble Beach is a golf course that I would pick for me.

"I've got Colonial next week which is going to feel like a pitch-and-putt by comparison, then the Canadian Open.

"I have some great stuff ahead of me. I'm feeling a bit bruised and battered but I have to say, the game is OK and I'm looking forward to the next few weeks."

Rory McIlroy was hoping to scrape a top-10 finish after a closing round of 69, the four-time major winner having been seven over par after just three holes of his second round.

"I've moved up the leaderboard quite a lot and my goal at the start of the day was to get into the top 10," McIlroy said. "I played well and it was a good way to finish off the week.

"I stuck at it the whole way. It's a 72-hole golf tournament and you've got to try till the very end and I did that this week.

"You know, it wasn't good enough to be up there in contention but I made improvements each and every day, which is a good thing."