A day after Roger Federer lost, and we're still searching for answers

Flashback: Federer falls to Millman in four sets (2:34)

No. 2 Roger Federer wins the first set but loses the next three, including two via tiebreak, in falling to John Millman in the US Open's fourth round. (2:34)

NEW YORK -- Labor Day produced a pair of sensational upsets at the US Open. Maria Sharapova lost to Carla Suarez Navarro, then Aussie journeyman John Millman shocked No. 2 seed Roger Federer before a disbelieving crowd on Arthur Ashe Stadium.

Federer won the Australian Open in early February but hasn't reached a Grand Slam semifinal since or prevailed at a Masters Series event. His loss at Flushing Meadows leaves some burning questions in its wake, and we'll try to answer them, with help from US Davis Cup captain and four-time Grand Slam champion Jim Courier:

1. Is Federer entering a new, final phase of his career?

Forget the "R" word. It's not going to happen. But it's pretty clear the astonishing momentum Federer built following his hiatus of 2016 is slowing. It shouldn't be surprising; he's 37 years old and nobody can sustain his brand of dominance forever. Federer is 3-3 in finals this year, winning his last title in June on the Stuttgart grass. He has a load of points to defend in the fall, so he'll need to lift his game to keep his ranking high.

The challenge for Federer going forward will be to sustain his production while playing a selective schedule that omits clay and some Masters Series tournaments altogether. He'll need to do well when he does play to keep his ranking up.

Courier's take: "I wouldn't consider this result a turning point. I'd say he's still in the stage he entered when he switched to a new [larger-headed] racket and eliminated clay from his schedule. The conditions were very difficult on Monday night. They surprised him a little bit. He probably didn't expect to feel like he did."

2. Who's the great beneficiary of Federer's loss, besides Millman?

In the short term, the obvious answer is Novak Djokovic. One of the major obstacles that challengers of the Big Four have faced over the years is that beating one of those icons requires a great effort, but beating two or even three of them in the same event -- especially back-to-back -- is near impossible. Whenever one of the icons drops out of a draw, it increases the odds of an outsider doing well -- even more than it greases the rails for a fellow Big Four member.

Courier's take: "Novak. Clearly, the likelihood of Millman backing up that performance against Federer is not high. He's never even had a top-10 win before. Two things will make Novak's path easier going forward: He's gotten through the heat [he'll have a night match Wednesday], and the obvious one: He won't have to play Roger.

3. If Djokovic and No. 1 Nadal were to play in the final, who would you pick?

This may be the most compelling question hovering over the tournament at the moment, right up there with whether Serena can win it all. Both men have looked good against comparably decent opposition. Nadal, the defending champ, seems to have had less difficulty with the heat and after a dismal first set Tuesday against Dominic Thiem, played with a spirit that led him to a thrilling win against Dominic Thiem.

Djokovic is coming off that career-reviving win at Wimbledon, backed up by a triumph at the Cincinnati Masters. He's on a 10-match winning streak and 19-1 since winning Wimbledon. Nadal is 27-1 since the start of the Rome Masters. His lone loss came against Djokovic in an excruciatingly close Wimbledon semifinal. Both men have lost just two sets so far.

Courier's take: "If it's hot and humid, like today, I like Rafa. If not, if it's going to be cool like they say on Sunday, then Novak. If the temperature is going to be in the 70s, it will slow the court down. Rafa's ball won't jump as high, and we know Novak is pretty balanced. He'll be able to get on top of that ball. Plus he's confident again.

4. Is Roger Federer jinxed in New York?

Let's face it, Wimbledon loves Federer. Melbourne and the Australian Open love Federer. The French Open still loves Federer even though he doesn't play there anymore. But the US Open seems to have it in for the man, even though he won the event five successive years ending in 2008. Since then, he's won every other major at least once while only making one US Open final. All kinds of things have gone wrong for him. Match points blown, losses to journeymen, Novak Djokovic, a bad back. So yeah, maybe New York just doesn't like nice guys.

Courier's take: "Yes there is, but maybe it's all driven by a Federer-Nadal jinx. It's amazing that New York fans have never seen a meeting of those two in the US Open. Federer's recent record at the Open is surprising because the surface is playing pretty quickly. And he's had many near misses, single points that could have changed this storyline. But here we are. Having said that, the nighttime loss to Millman was not about luck; it was about conditions.