Ireland's Shane Lowry is relishing the chance to claim a first major title after surviving a marathon third day of the 100th US PGA Championship.

Lowry was one of the 78 players who had to complete their second rounds on Saturday morning after bad weather on Friday, but produced a superb 64, his lowest score in a major, and followed it with a third round of 69 at Bellerive Country Club.

That left the 31-year-old four shots off the lead held by Brooks Koepka and in position to exorcise the ghosts of 2016, when he led by four after 54 holes of the US Open only to struggle to a closing 76.

"I said to Alan [his brother and caddie] walking into 18, make birdie here and we have a right chance tomorrow and that's what we did," Lowry said. "I feel like I'm where I want to be.

"I'm very excited for tomorrow. It's great to have your brother on the bag, your dad out there watching and you're going and competing in the final round of a major. It doesn't get much better so I'm looking forward to it.

"I just have to play my own game and just be patient. Yes, it is a course (where) you can make birdies, but I just think this afternoon there's been a couple of big numbers as well.

"I didn't feel like I had my A game out there this afternoon, but I did well to kind of shoot the score I did. And hopefully I go out and play decent tomorrow and see what happens.

"A late tee time tomorrow on a Sunday at a major is where I want to be. I've been in this position before, so I know what it's about. Hopefully I can go out and do a better job this time than I did the last time."