Rustiness proved massively costly for Nike’s $100 million man Rory McIlroy as he lost his world No 1 crown to Jordan Spieth in the US PGA at Whistling Straits.

He might have made a miraculous comeback from the ankle injury that forced him to miss his defence of The Open and the WGC-Bridgestone Invitational. But even after rushing back to try and retain the Wanamaker Trophy and stop Spieth taking over at the top of the world rankings, his lack of sharpness around the greens proved he's human after all.

A closing 69 left him in 17th spot on nine under—a hugely impressive result. But Spieth finished second on 17 under, three shots behind new champion Jason Day, to become the 18th player to reach No 1 in the world and end McIlroy's most recent reign after 53 weeks.

Around 90 minutes before he was deposed by Spieth, McIlroy was asked about the possibility of losing the No 1 spot and said: “Honestly, the way Jordan has been playing and the way I haven’t played much this year, I think if he does go to No. 1 today, it’s very deservedly so. 

“Winning two majors, winning a couple other times this year, had a chance at the Open, has a chance obviously today. 

“And if he was to get to No. 1 today, I’d be the first one to congratulate him because I know the golf you have to play to get to that spot, and it has been impressive this year."

Even though he is already playing catch up with a short game wizard like Spieth, McIlroy was well below his best in Wisconsin.

Of the 20 times he had to scramble for his par, he converted just 11, which left him well down he field in that department.

That said, a Top 20 finish after 53 days away from competitive action was still a sensational  performance.

But even McIlroy is human and there were simply too many ahead of him for his hopes of a final day comeback to come true.

"I feel like I did well," McIlroy said. "Obviously coming back after the lay-off, not hitting a competitive shot in two months, shooting nine under was a decent effort. 

"I didn’t see 19 under winning this week. I thought something between ten and 15 but it just shows you how high the standard is these days. But first week, coming back, I thought I did pretty well.”

He admitted his ankle swelled up overnight but insisted it didn’t hinder him on the course.

Planning to take the next two weeks off to do more rehab and practice before returning for the second FedEx Cup event in Boston, he said: “Overnight the ankle did swell a bit, but once I got it moving and compressed it a bit, it was fine.  

"It probably won’t look like a normal ankle for two or three months, but there is no pain in it, which is the main thing.

"We came up with a plan that after this week I could take a couple of weeks off just in case anything did happen or there were any setbacks. 

"I’m just going to take a couple of weeks off and not need a strap or anything to play. And then after that I’ve got another week off, so by the time I’m in the middle of September, there will be no issues and hopefully I can give it a good run in the FedEx Cup. 

“I felt like I give it a good run this week and the ankle is in good shape.”

McIlroy's game is also in remarkably good condition but he could never hope to beat the likes of Day and Spieth after 53 days without hitting a competitive shot.

As he walked to the first tee, a cop said: “Best of luck Rory, gonna be windy later.”

McIlroy replied: “Let it blow.”

But it didn’t blow enough to trouble the leaders early on and the McIlroy birdie whirlwind failed to materialise.

While he was in trouble only once — he avoided a three putt bogey at the short third by draining a seven footer—the first five holes were quiet.

He missed chances from 20 feet at the first and 10 feet at the second and then drove into sand at the fifth and only made par.

His luck finally changed at the driveable sixth, where he hit a spectacular recovery to 10 feet from the right rough and rolled in the birdie putt.

A two at the 221-yard seventh got him to eight under and gave his fans hope that he could launch a miraculous comeback.

But missed chances from 18 feet at the eighth and 13 feet at the ninth left him playing catch up.

As the turned for home, Day, Spieth and the rest of the leaders were in the red and moving away.

And while he showed glimpses of his brilliance, reducing the 361-yard 10th to a drive and a 40 yard chip to 18 inches. there were too many signs of rustiness.

At the par-five 11th he found the edge of the green in two but took three more shots to get down for his par.

Then at the 13th, he drove into sand, thinned his second over the green into deep rough and left a 18 footer for par well short.

At the 14th he had a 14 feet for birdie after a nice wedge but his putt never threatened the hole.

A two putt birdie at the par-five 16th showed his power his still there but he only got up and down once from bunkers all week, saving par at the 17th, before pitching and putting for another good par at the last.

Pleased overall, McIlroy said: “I thought, between 10 and 15-under would have a great chance to win, but obviously the standard is just so high these days that I didn’t see close to 20-under par winning this tournament.

"I'm looking at it as a whole, I feel like I've done well to come back and shoot the scores that I have. I feel like I progressed each and every day.

"I'm walking away pretty happy with how the week went. Obviously it isn’t a win and didn’t get myself into contention, but considering six weeks ago I wasn't able to walk, it's not a bad effort.

“I just need to sharpen up around the greens and be more efficient when I give myself wedges in my hand.

“Getting those two balls up and down on 17 and 18, that’s something that comes with just playing a bit more and just having experience with certain shots and certain lies.”

Spieth closed with a 68 but his 17 under par total was only good enough for solo second behind maiden major winner Day, who played aggressively and won by three strokes on 20 under par 268 — the lowest 72-hole score in relation to par in the history of major championship golf, beating the record of 19-under set by Tiger Woods during the 2000 Open Championship at St Andrews.

"It's by far the best consolation, by far the best loss I think I've ever had," Spieth said of getting to world No 1 on the day he came up short in his bid to win a third major this year.

"I played solid golf. I played 11-under on the weekend off of the tough draw the first two days and still had a chance to really win. Although the key holes were 8 through 12 for me today where I really needed to make a statement and couldn't get it to go, I still provided some opportunities to maybe put pressure on at the end and he just shut the door.

"He was sitting there swinging as hard as he could off the tee, and every single drive was right down the middle of the fairway. I think he missed two shots today and he made two bogeys off of that. But the ones he capitalized on were good enough.

"The fact that I would have had to shoot 7- or 8-under to win, if you told me that at the beginning of the week, I'd have told you I missed the cut. A lot of positives come out of today. To be No. 1 in the world as a team is fantastic. Certainly it was a lifelong goal of mine, and that was accomplished today."

Spieth was 54 under par for the four majors this year, winning the Masters and the US Open and finishing fourth in the Open and second in the US PGA to shave a shot off the previous aggregate low set by Woods in 2000.

As for Day, his victory was an emotional one.

"The path that I was on was never expected for me to be here where I was today," Day said. "I lose my dad at 12, and then meet Colin (Swanton) and have him walk the journey with me and have him walk up the 18th hole with me was just a special, special experience that I could never forget. It's just an amazing feeling I have."

Admitting he found it hard to focus, he said: "There were plenty of times when I got out of it, more so just thinking about the future, especially on the back side there were a few times where I had to pull myself back in and say it's not over, you've got to keep grinding, keep fighting.

"And once I did that I kind of pulled myself back and started hitting the quality shots that I needed to. Just to be able to finish with a birdie on 16 and two pars on 17 and 18 felt fantastic."

Told of his record low aggregate, he said: "I did not know that. That was a pretty amazing accomplishment. But that does feel good. I never knew that I set the record. It's a fantastic record to hold. There's been such amazing golfers, especially throughout the history of golf, our sport, and to have that record just goes to show the work I've put in is paying off.

"It didn't feel like work, it felt like I was mentally and physically grinding it out as hard as I could. I wasn't going to stop fighting until it was over.

"I enjoyed the 18th hole when I had about a half foot putt, so that was fantastic. It was a fantastic day for me, personally, and something I'll never forget."