Jack Nicklaus has been a huge fan of Rory McIlroy’s for quite some time but even the Golden Bear was bowled over by the Holywood star’s dramatic back nine comeback to win his fourth major at Valhalla on Sunday.

The 18-time major winner insisted last week that McIlroy had the game to win between 15 and 20 majors, if he had the inclination. 

And he saw nothing in the final round of the US PGA to dissuade him from that view as McIlroy came from three shots behind with nine holes to play to win by a stroke from Phil Mickelson.

Nicklaus was hugely entertained by the great “theatre” of the final day that saw up to five players share the lead at one stage before McIlroy got back in the mix with that eagle three at the 10th and then put his foot on the accelerator over the closing holes.

“Fantastic,” Nicklaus said of the final round. “It was really a great tournament. It was great theatre. Great golf, actually. It was one of the best tournaments to watch—because of such good play—that I have seen in a long, long time. 

“Henrik Stenson played fantastic… Phil Mickelson was unbelievable. Just pure guts and really great golf. And Rickie Fowler was simply terrific. He played well all the way down the stretch, until he couldn’t see at 18. No one could. So let’s just discount what happened at 18, because I just thought Rickie was terrific.

“Then Rory, who got three shots down, showed so much poise, confidence and determination coming down the stretch. The tee shots he hit today, wow. Early on, Rory was just playing along and couldn’t get anything going (2 over after six holes). 

“All of a sudden, everybody else was getting something going. Then Rory got the right break at the 10th hole with a great shot—he made the right break at 10 with that second shot (to set up eagle). He was off and running from there.”

Nicklaus has become something of a mentor to McIlroy in recent years and sees no limits to the young Ulsterman’s potential.

“I think Rory is an unbelievable talent,’ said the Golden Bear, who holds the all-time record with 18 majors.

“It depends on what he feels his priorities are but I think he has the opportunity to win 15 or 20 majors if he wants to keep on playing.

“I love his swing, his rhythm, his spirit. He has got a little swagger there, it’s a little bit cocky but it is not offensive. I like that self-confidence in a young man. He’s got an unbelievable amount of speed in his golf swing. He obviously hits it a long way but he does it consistently, with control.”

McIlroy has tried to flee from high expectations and said earlier in the week at Valhalla that his ambition was simply to get to four majors.

“If that’s Jack’s opinion of me, he has a high opinion of me. I’ve always said I’m on three, and I want to get to four. Hopefully I can get to four this week and then keep going from there,” he said.

The world No 1 did not change his opinion on Sunday night, though he did insist that his next goal is to try and become the most successful European major winner of all time.

“I think I've got to take it one small step at a time.  I think the two next realistic goals are the career Grand Slam, and trying to become the most successful European player ever,” he said. “So Nick Faldo, most successful European ever in the modern era, Nick Faldo has six. Seve has five. Obviously the career Grand Slam coming up at Augusta in eight months time or whatever it is, they are the next goals.

“And hopefully, when I achieve those, I can start to think about other things.  But right now, that's what my focus is.  My focus is trying to complete this year Grand Slam and then move forward and try and become the most successful European ever, and hopefully in time, if I can do that, then I can move on and set different goals.”