The brilliant Brooks Koepka was threatening to turn the US PGA Championship into a one-man tournament as he birdied three of his first four holes on Friday to open up a five-shot lead at Bethpage.

By the time the reigning champion teed off on Friday, having carded a sublime, seven-under 63 the previous day, his advantage stood at two strokes, with Jordan Spieth shooting 66 to move into second.

Koepka wasted no time in pulling further clear, though. Gains on his first two holes were followed by another at the par-five fourth, lifting the three-time major winner to a scarcely believable score of 10 under on a course renowned for its difficulty.

He could even have registered an eagle at four after hitting his second shot to 17 feet.

There was still plenty of time for things to change, particularly with challenging winds forecast for the afternoon wave, but the American was looking unstoppable.

Spieth's four-under round on Friday left him one ahead of Daniel Berger and Dustin Johnson, who shot 66 and 67 respectively. Tommy Fleetwood duly birdied the eighth to join Spieth at five under.

Rory McIlroy slumped to seven over at one point but looked likely to have done enough to make the cut at plus three after registering four birdies on his inward nine.

Also at three over was Masters champion Tiger Woods, playing alongside Koepka and still in the early stages of his second round.