Rory McIlroy displayed immense grit and patience to keep their PGA Championship hopes alive but know they'll need to make a move on Sunday to catch Brooks Koepka and add to their Major tallies at a rain-soaked Oak Hill.

The Holywood star made five birdies in a 69 to sit alone in seventh on two-under-par, leaving him just four shots behind Koepka in seventh as Lowry chipped in for a 71 that left him tied 10th on one-over, six shots behind.

"Look at Justin Thomas last year," Lowry said, recalling how the American came from seven shots behind Mito Pereira to win at Southern Hills last year.

"I always say about Majors, you just need to hang around. Just hang around. Make yourself a nuisance to somebody. Hang around, and hopefully, you'll get to do something tomorrow afternoon."

Koepka made 131 feet of putts and five birdies in a second successive 66 to lead by a shot on six-under from Viktor Hovland and Canadian Corey Conners, who ran up a double-bogey six at the 16th after burying his second in the grassy face of a fairway bunker and shot 70.

"It would mean a lot," Koepka said of the thoughts of a fifth Major win that looked unlikely when he was struggling with injuries in recent years and defected to LIV Golf.

"I think a major championship would mean a lot to anybody. So yeah, to win one would be fantastic.”

He’s won three of his four Majors from the 54-hole lead and he’ll be looking to extend his advantage.

"I mean, I was just told that I think only Tiger and Jack have won three (PGAs), so that would be pretty special to be in a list or category with them. Just got to go out and go play good tomorrow."

Bryson DeChambeau is just three shots off the lead after a 70, while Justin Rose battled for a 69 to share fifth on two-under with overnight leader Scottie Scheffler, who had 34 putts in a 73.

Under the weather on day one, McIlroy has yet to find his A game, but he's displayed great acceptance and patience and knows that if he can eliminate the bogeys on Sunday — he had four yesterday, two on Friday and four on Thursday — a 65 could be a nuisance to Koepka and the rest.

"I still don't feel like my game is in great shape," said the Co Down man, who will looking to end a near nine-year Major drought in upstate New York alongside club professional Michael Block, whose fairytale week continued with a third successive 70.

"I've held it together well. I've held some good putts. I've scored well.  I probably hit it a little better off the tee today than I did the first couple of days, but I think this tournament and especially in these conditions and on this golf course, the non-physical parts of the game I think are way more important this week than the physical parts of the game, and I think I've done those well, and that's the reason that I'm in a decent position."

McIlroy made two stellar twos at the third and fifth but bogeyed the sixth, eighth and ninth to turn in one-over.

But he never stopped grinding and took advantage of his power to birdie 12th and 13th by hitting short irons inside six feet.

He couldn't take advantage of his power at the 14th, then saved a great par from 12 feet after a shoved tee shot at the 15th before making a seven-footer for birdie at the 16th to get within four of the lead.

He did well just to drop one shot at the 17th, where he overshot the green in three but made a five-footer for bogey.

And with just six players ahead of him — albeit five of them are Major winners — he knows he's got a chance of winning that elusive fifth Major with a 65 or possibly less.

"I hope so," he said. "Like, if I look at today, I made enough birdies to shoot a score like that. I just needed to keep those mistakes off the card.

"I need to keep hope. I have to believe that there is a score like that out there because, looking at the board, it's probably a score I'm going to have to shoot something like that to have a chance to win."

Lowry played conservatively all day, but while the scorecard says he birdied the sixth and bogeyed the seventh and 14th, it was a round full of incident.

At the 14th, he took four to get down from sand, 10 yards from the pin, but made amends for that mistake at the last, fist-pumping joyously after chipping in from up against the collar of rough for par.

"I felt like I was quite good, conservative; it was tough out there, and I knew pars were going to be good," Lowry said. "I felt like I never really got it going forward; I gave myself a few chances, 25 footers, hit some great putts that just missed, but 14 was a killer.

"I had played conservatively all day, but to do that out of the bunker was just silly. Then to go and miss a three-footer for birdie on the next, you feel like you are hanging on. One-over looks pretty good. It still has somewhat of a chance.

"I was happy to par the last two; overall, I am pretty happy. I just played the game very well today and did what I needed to do, and then 14 and 15 were kind of the stage of the round where I could have got it going, but I managed to hold on 16, 17, 18 — three pars, three tough holes to finish."

As for a Sunday charge, he knows he has the firepower.

"I made seven birdies yesterday, so a low round is definitely in me. It is the major championship Sunday; it is what you practice for.

"You can play your way out of a tournament on a day like today, and I don't think I have done that. If I can go out tomorrow and do a good front nine, all of a sudden, you are in the tournament going into the back nine of a Sunday. It was great out there with Rory, great atmosphere."

As for Pádraig Harrington, the veteran (51) was heading for his highest score in a Major when he turned in eight-over 43.

But he fought back to come home in 32, holing a 25-yard bunker shot at the 18th for birdie and a five-over 75 that left him tied 58th on eight-over.

"I three-putted the first two greens, and on a tough day, you need momentum," the 2008 champion said. "Every day you are on the golf course in a situation like that is a practice day, a training day, so you are trying to do things right.

"You are trying to dig deep; once you know you can't win the tournament, it is all about every shot is practice, training.

"There is no substitute for hitting shots with a card in your hand. You can hit as many shots as you like on the practice range, but there is no substitute for playing real golf.

“That's what you see when you go into the back nine like that is an opportunity to get your game in shape. I was trying to break 80."

The cheer for Harrington's bunker shot was only exceeded by the reception for PGA professional Michael Block, who shot a third successive 70 to share eighth place with Justin Suh on level par and earn a dream date with McIlroy.