As the last tennis major of the season gets under way in Flushing Meadows tomorrow, the four tennis superpowers who have shared 36 of the last 38 Grand Slam titles now find themselves in altered circumstances.
For a start, due to Rafa Nadal's ongoing wrist problem, the "fab four" are down to three - Novak Djokovic, Roger Federer and Andy Murray - and the 27-year-old from Dunblane is regarded as only the eighth most likely to reign in Queens this fortnight. And it isn't easy to argue on the Scot's behalf.
This has been an uncertain, troubling year for the man who won this championship so memorably in 2012. A combination of rehabilitation after back surgery, a self-confessed drop in his motivation, a high-profile coaching change, and poor form means Murray hasn't won a tournament, nor even beaten a top-10 player, since taking the Wimbledon title in 2013.
While it would be folly to dismiss the British No 1's chances completely for any tournament, particularly one where he feels so at home, that badly-needed, confidence-bolstering win continues to elude him and he has been placed in a fiendishly difficult section of the draw. In all likelihood, Jo-Wilfried Tsonga, the resurgent Frenchman who has recently reeled off four back-to-back victories over top-10 players, including Murray, in the space of a week, and Djokovic must both be outmanoeuvred just for the Scot to reach the semi-finals.
"I'm sure he would be the first to tell you that he has had a disappointing year and he hasn't come back as quickly from the back surgery as he would have liked," said Murray's former coach Brad Gilbert, now a pundit with broadcasters ESPN. "More than anything since Wimbledon he has really struggled against top-10 opponents and looking at his draw, I am not sure that anyone could have slotted in a more difficult one for him. But he works unbelievably hard. At some point he is going to figure out his losses against top-10 players. Once he does that, I believe for sure by 2015 he will be back among the top four players in the world."
Gilbert's broadcast stablemate Patrick McEnroe is even more circumspect about the Scot's chances. "It does come down to confidence," he said. "Murray is a pretty emotional guy and with [coach Ivan] Lendl leaving that must have been pretty difficult for him. It was natural that he would have a let-down following Wimbledon last year.
"But he couldn't have gotten a worse draw here. Even Federer, who he is 11-11 with in his career, I think he would have preferred to play over best-of-five than Djokovic in the quarter-finals. And he has a pretty tough draw to even get that far. Quite frankly I don't expect him to make a huge run at the US Open, but I am sure he will be back, although whether I expect him to be back in the top four is debatable. Can he find that extra motivation that he is going to need? He is not like Federer, he can't just go out there and free wheel."
Djokovic has also had his challenges, even if they seem like a walk in the park compared with those of the Scot, with whom he practised in Flushing last week. Since putting his recent hoodoo in major finals behind him in that breathless showpiece at SW19 this summer, returning to the top spot in the world rankings in the process, the Serb finally seems to have exhaled and caught up with life.
He married his childhood sweetheart Jelena Ristic in Montenegro in July, with the birth of the couple's first child to follow before the end of the year. While the 27-year-old will surely sharpen up his act in the Big Apple, tennis appeared something of an afterthought in uncharacteristic defeats to Tommy Robredo and Tsonga in the US hard-court swing.
Amid these varying degrees of uncertainty and upheaval, only one member of this awesome foursome truly stands tall. The trademarked Greatest Player of All Time's credentials to record his 18th Grand Slam title have never been more alluring, even with two sets of twins in tow. In late January, Federer was ranked as far back as Murray is now, but the 33-year-old is fresh from victory in his first Masters event for two years, and is to be admired as much for his quantity as his quality.
While the stresses and strains of the sport have broken down many a younger body, incredibly the US Open will be Federer's 60th successive Grand Slam, a run which stretches back to 1999, when he was just 18. Having re-invented himself as a modern serve-and-volleyer with the help of Stefan Edberg, should he succeed this fortnight, only two men, Ken Rosewall and Andres Gimeno, will have won a major at a more advanced age in the Open era.
"To do that, 60 majors in a row, is heroic in a way," says John McEnroe, the US tennis legend turned ESPN pundit. "It's obviously remarkable and unbelievable that he's been able to do this consistently well for this long. That should not be underestimated or under appreciated by tennis fans. He's stepped up every single time."
"For me his longevity is just off the charts," added Gilbert. "There is no foolproof system not to get hurt, yet in 18 years he has had no serious injuries. He has obviously done an amazing job of taking care of his body, and plays an incredibly wise schedule. He seems to be able to play without barely sweating. When he plays on clay he doesn't even have any dirt on his socks!"
The sense of flux amongst the "fab four" lends an unpredictable edge to this tournament, and gives hope to those who fancy filling the void. If Stanislas Wawrinka, one of the two men capable of disrupting the quartet's stranglehold over the majors, has appeared unable or unwilling to fully capitalise on his Australian Open victory in January, the name of Tsonga must be near the top of this list, and you can also include Wimbledon semi-finalist Grigor Dimitrov and the top-ranked North American in the draw, Canada's Milos Raonic. A not-entirely convincing home challenge will be headed up by the likes of John Isner and Jack Sock.
"Now it's three," said McEnroe, "and Murray is not at the level he was, although he has a shot now to re-establish himself. The question with Dimitrov is somewhat physical: is he ready to do it on a hard court as opposed to the grass court where his talent was able to shine through a little bit more easily? Raonic wants to prove he's not a one trick pony, that he doesn't just have this awesome serve and big hitting. Wawrinka won it [a Grand Slam] and he hasn't been the same since. He doesn't seem to be able to handle the attention."
His more vaunted countryman, however, adores the centre stage. It is likely he will embrace the limelight, maybe or maybe not for one last time, in New York this fortnight.