Northern Irish golf star Rory McIlroy played such a sublime second round of golf at the PGA Championship that he had defending champion Alex Noren quipping about early retirement.

The 29-year-old quadruple major winner carded a bogey free seven-under par 65 to move to 12 under and a three-shot lead over young Englishman Sam Horsfield and French journeyman Sebastien Gros, who came in late in the day with a superb 66.

Noren — who played in the same group as the Ulsterman and, like him and playing partner Lee Westwood, stayed clear of bogeys — may have been joking about quitting. But he was in awe of McIlroy’s round.

“That’s the best round I’ve ever seen. I’m about to quit golf I think,” said Noren.

Noren sits five shots off McIlroy but the Swede will be well aware that after his stunning 62 last year, which saw him come from way off the pace to seal victory, anything is possible.

McIlroy, though, likes being out in front going into the weekend even if he, like Noren, staged a last-round blitz to come from seven shots off the lead to win in 2014.

“Obviously I have the confidence that I’m playing well and I can go out and try to, I guess, just replicate what I did the day before,” said McIlroy.

“On the first tee box tomorrow (Saturday), I’ll be thinking about what I did today and trying to just keep the same thoughts and make the same swings.

“You know, I went a couple better today than I did yesterday. (I am) not sure I’ll keep the same progression going but something similar tomorrow would be nice.”

– ‘Hard to catch’ –

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McIlroy’s only disappointment was parring the final two holes, both par fives, as he had done on Thursday but he was one of many who came away with nothing from them with Horsfield dropping a shot on the 17th and parring the 18th.

The 21-year-old Horsfield, who has had an encouraging start in his rookie season posting two top-four finishes, said he could cope with the pressure at being among the frontrunners at such a high profile event.

“I think any time you’re playing on the weekend and you’re up there near Rory, I think you’re going to be doing pretty well,” said Horsfield.

“I’m just looking forward to tomorrow, whether I’ll be playing with Rory or whoever I end up playing with, I’m going to go out there and give it my all.”

Horsfield’s gut feeling is the title will come down to who putts best. If that proves the case Thailand’s Kiradech Aphibarnrat — five shots off McIlroy — should be confident.

“I’ve been putting so good,” said the 28-year-old.

“I hole everything inside 15 feet which is phenomenal.

“Just have to keep doing until the last two rounds to catch Rory.”

One man who knows McIlroy inside out is his fellow Northern Irishman Graeme McDowell, with whom he formed a partnership in the 2010 and 2012 Ryder Cups. They were known as ‘G-Mac’ and ‘Little Mc’.

McDowell, named a Ryder Cup vice-captain on Tuesday but still keen to qualify and compete in France in September, is six shots back from his compatriot.

The 38-year-old said chasing down McIlroy would be a tough ask: “You know, when Rory is on his game, he’s incredibly tough to catch.

“I know he likes it around here, having won here in the past, and these are perfect conditions for him. Obviously no wind, target golf; he can use his length and his ball flight control to his great advantage.

“But obviously I’m hoping to give him a run for his money this weekend.”