Where once it looked as if Rory McIlroy’s ownership of the world number one spot would be long-term, with the potential to rival the longevity of Tiger Woods’ stint at the top, such

speculation would now appear to be as reliable as the Chinese stock exchange.

Ironically, McIlroy returned to number one in a week where he didn’t hit a competitive shot, after deciding to bypass the Barclays, but he resumes tournament play at this week’s Deutsche Bank Championship aware that he has not one but two possible usurpers.

Jordan Spieth and Jason Day have, between them, stolen much of McIlroy's thunder as summer moved on into autumn, and the American and the Australian each head into the Deutsche Bank – which starts on Friday, finishing on Monday, which is Labor Day in the US – with the opportunity to make the Northern Irishman's latest stint at the top a short-lived one.

The benefit of two weeks on the sidelines should have further aided McIlroy’s rehabilitation from the ankle ligament rupture he suffered in early July – which forced him to miss both defences of the British Open and the WGC-Bridgestone Invitational – and he knows that a strong performance in the remaining three FedEx Cup playoff tournaments could yet reap dividends, financially as well as laying down a marker as to who is the world’s number one.

Overtaking McIlroy

Spieth spent much of the year chasing and eventually overtaking McIlroy in the official rankings, albeit for just a two-week period, but the race is now a three-pronged one.

For Day, the hottest player on the planet just now with three wins in his last four outings, including a breakthrough Major title in the PGA at Whistling Straits, to move to number one he would need to win the Deutsche Bank at TPC Boston and McIlroy and Spieth finishing outside the top three.

For sure, Day – winner of the Canadian Open, the PGA and the Barclays in a marvellous spell – has the number one spot in his sights.

“I never thought I’d have the opportunity, mathematically, to get to number one. It’s been a goal of mine . . . the only way I can control it is through playing good golf, that’s what I need to focus on [and] let the rest take care of itself.”

Committed

Day’s win, the fourth of the season, moved him to the top of the US Tour’s FedEx Cup standings ahead of Spieth, who missed the cut in New Jersey. McIlroy’s absence from the Barclays saw him drop from ninth to 15th, but the Co Down man is committed to playing all three remaining tournaments – the Deutsche Bank, the BMW in Chicago and the Tour Championship in Atlanta – to have a chance at that $10 million bonus payday.

“I have the opportunity to get to number one if I play some good golf over the next three or four weeks. It’s been a goal of mine. But it’s going to be tough to catch. Right now I’m trying to focus on getting some rest and going into [Boston], trying to play that golf course, which I absolutely love. All positive stuff,” said Day, who believes that McIlroy and Spieth will enter the run-in fresher.

He observed: “I played with [Spieth] the first two rounds . . . visually you could see that he was tired . . . [and] with Rory missing [the Barclays], who knows what happened to his ankle, or if it was something where he really needed to rest it. So those guys are going to come in fresh [to Boston].”

Day’s run of form of late has been quite remarkable. He has finished 1st-1st-12th-1st in his last four outings; and, for his last five tournaments, he has been 73 under par.

“The synergy between my body and my golf swing is matching perfectly. That’s where I can just get up there and I can rip at it, get the ball down as far as I can. The short game has been great,” said Day.

With Pádraig Harrington failing to survive the cut at the Barclays, the Dubliner has missed out on advancing to Boston and his interest in the FedEx Cup has ended for this year.

On the European Tour, there will be six Irishmen in action in the Russian Open: Damien McGrane, a runner-up in the tournament last year, is joined by Kevin Phelan, Peter Lawrie, Niall Kearney and Brian Casey, who has received a sponsor's invite.