Jason Day will have to overcome a marathon third day if he is to claw his way back into contention at the US PGA Championship in Missouri.

While countryman Adam Scott is safely in the clubhouse five shots off the pace, Day was among the half of the field who failed to complete their second rounds before play was suspended for the day due to dangerous weather.

Scott fired a five-under-par 65 at Bellerive Country Club to earn a 36-hole score of five under, while Gary Woodland (66) took the clubhouse lead at 10 under, with fellow American Kevin Kisner (64) one shot further back.

US Open champion Brooks Koepka fired a blistering 63, equalling the PGA Championship record for lowest round, to leapfrog into outright third at eight under.

Although a former winner of the Masters, Scott said his motivation to move further up the leaderboard was his lacklustre record at the PGA .

Scott has just four top 10 results from 17 previous starts.

"I don't really feel I have ever been in contention on a Sunday at the PGA, although I've had some good results," Scott said.

"I'd like it to be kind to me this weekend."

Playing in the afternoon wave on Friday, former world No.1 Day was only beginning to make his move before the weather suspension.

He reached the par-5 eighth hole in two shots and two-putted for a birdie to climb to four under and six shots off the pace.

After two more solid shots at the par-4 ninth, Day will face a 22-foot birdie putt when play resumes.

Day, the 2015 US PGA Champion, will have to complete the back nine of his second round on Saturday morning with threesomes going off two tees, before the third round starts.

But he is no stranger to mammoth rounds at the year's final major, having endured a 36-hole last day during his title defence at the 2016 edition - when he finished runner-up to Jimmy Walker by one shot.

Marc Leishman sits at one under following a disappointing 71.

Australian club pro Craig Hocknull (three over) and Cameron Smith (four over) will also complete their second rounds on Saturday and will have to work to sneak inside the projected cut line of even par.