“Honestly the way Jordan has been playing and the way I haven’t played much this year – I think that was only my 12th or 13th event – it’s very deservedly so,” said McIlroy, who had not played since the US Open in June after rupturing an ankle ligament playing football with friends on July 4.

“Winning two majors, winning a couple of other times this year, had a chance at the Open, had a chance 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.”

Asked if regaining top spot would give him extra motivation, McIlroy added: “Not really. I’ve always said that winning golf tournaments takes care of all of that stuff. Right now I’m focused on just getting my game the way I think it has to be to win tournaments like this.”

Spieth, 22, who becomes the second youngest world number one after Tiger Woods, said: “It feels really good. It’s an unbelievable feeling.

“I knew walking up the 16th Jason was going to win so I was focusing on finishing second and accomplishing a career goal. So much work has gone into this and what a year it has been.”

McIlroy was left to rue rounds of 71 on Thursday and Friday which left him too much to do, but added: “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.

“If I was to take back anything of this week, it would just be probably that second day when we teed off in benign conditions in the morning and I didn’t take advantage of that.

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

McIlroy said his ankle had responded well to the difficult terrain at Whistling Straits, adding: “It’s been great, honestly. I’ve had no discomfort with it at all.

“I’m still rehabbing it whenever I get back, I’m still doing exercise on it every night and every morning, getting treatment on it. But it’s good.

“I’m hitting it the same distance as I have been, and able to get around 18 holes very easily. The residual swelling that just sort of comes from activity, that probably won’t go away for another two or three months, but it’s nothing to worry about.”

McIlroy will skip the first FedEx Cup play-off event and return to action in the Deutsche Bank Championship in Boston from September 4-7.