There is one question and one question alone dominating the men's section of the US Open: can anyone stop Novak Djokovic?
The Serbian was won the Australian Open, Roland Garros, and Wimbledon already this year, meaning he will win a calendar slam should he take the US Open too.
That is something that has not been achieved for 52 years, and it would also mean a record 21st major title for Djokovic.
What is more, neither Rafael Nadal or Roger Federer are there to try and stop him, with both out injured. Nor is Stefanos Tsiitsipas, the world number three, who lost in round three.
If you think it's a mere formality for Djokovic to win the US Open, though, we are here to tell you to there are still plenty others who could deny him.
As Roger Federer and Rafael Nadal have declined, Medvedev has developed into the second-best player in the world.
The Russian is the most unconventional player on the circuit too, with his languid style, quirky sense of humour, unique technique, and movement that is rarely seen in a player so tall.
Medvedev has already reached a Grand Slam final this year too. That was in the other hardcourt event at the Australian Open. Novak Djokovic was at his brilliant best that day, meaning Medvedev is still awaiting his first major title.
However, he has fine recent form at the US Open too, where the quick courts really suit him. He reached the final in 2019 before losing a five-set thriller to Rafael Nadal, and was defeated in the semi-finals by eventual winner Dominic Thiem last year.
Medvedev did not lose a single set in his first three matches so far in this year's tournament, and has lost just 22 games so far which really highlights the kind of form he is in.
Zverev has been the apparent chosen one as far as the Next Gen are concerned for a while now, but he really seems to be approaching what could be a brilliant peak now.
The German is arguably the best and biggest server in men's tennis, and that means the conditions in New York this year will make him very tough to stop.
That was certainly the case last year, as he reached his first ever Grand Slam final in this event. He has recent form too, winning the Cincinnati Masters just before the US Open and the Olympic gold before that.
Unlike Medvedev, Zverev is in the same half of the draw as Djokovic, meaning he cannot face the Serbian in the final. However, it's worth remembering Zverev has beaten Djokovic in both the Olympics and ATP Finals, both on a hard court, so he knows he can get the best of the world number one on the big stage.
There is a serious argument to be made that Matteo Berrettini is the most underrated player in the men's game right now.
The Italian has gone on record saying he thinks he belongs in the same group as Medvedev, Zverev, Tsitsipas, and Thiem as the players best placed to end the dominance of the Djokovic, Nadal, and Federer triumvirate, and that is a big claim to make.
However, Berrettini reached the Wimbledon final this year, so there is definitely merit to that claim, and his big serve and forehand are perfectly suited to the conditions at the US Open.
There are question marks over his durability, it must be said. Injuries have blighted him before, and he does not seem to be the kind of player who can compete unless he's feeling 100% physically.
His path to the final is not easy either. He is due to run into Djokovic in the quarter-finals and even if he wins that then Zverev likely awaits in the last four.
That said, Berrettini is a player you take lightly at your peril, and he definitely has a shot here.
It is no secret that American men's tennis has been in the doldrums for some time now.
Certainly, the days of Andre Agassi, Pete Sampras, Jim Courier, and Andy Roddick dominating the ATP rankings are long gone, but Opelka has emerged as the new big hope.
It has to be stressed that Opelka is a serious outsider here. This is the furthest he has ever been at a Grand Slam, and he only has two career titles to his name so far.
However, there has never been a player in the ATP taller than the 6'11" American, and he puts every inch of that to good use with a brilliant serve.
That will get him plenty of free points and give him a chance against anyone, and his 2021 form has been very good.
There is also the home factor. The fans at Flushing Meadows are probably the most vocal in the tennis world, and they can give a big boost to home players.
There is no shortage of brilliant young players in men's tennis right now, and Sinner is perhaps the best of the lot.
He is certainly the best ranked of them, with the 20-year-old Italian establishing himself in the top 15 in the world this season.
Sinner is an aggressive power-hitter from the baseline, and the conditions at the US Open will help him.
The question, with so many young players, is the consistency. On his day, Sinner can compete with anyone, but he just doesn't have enough days yet.
He reached the final of a Masters level event this year in Miami, which shows he is capable of going deep in big events. It's hard to see him going all the way at the US Open, but he definitely has the talent and stranger things have happened.
Speaking of brilliant young tennis talents, we could not possibly ignore Carlos Alcaraz.
The 18-year-old Spaniard has carried the 'new Rafael Nadal' moniker ever since his talent was identified, but that is solely to do with nationality and very little else.
In reality, Alcaraz has a completely different game to that of Nadal, with his huge forehand the crown jewel in a vast array of weapons.
He showed what he is capable of in beating Tsitsipas in the third round. For context, no ATP player has won more matches that the Greek this season. He was in form and a genuine contender - and Alcaraz beat him.
Alcaraz is also helped by being in the weaker half of the draw. Medvedev is in it, but in terms of top-level talent that is just about it.
You've got to be realistic and understand that Alcaraz is a huge outsider. However, if you are a sporting romantic, then back Alcaraz and support him all the way.