Novak Djokovic came through a tricky quarter-final clash with Jenson Brooksby on Monday, which means the calendar slam is still very much on.
The world number one has now won four of the seven matches be requires in New York to become the first man for 52 years to win all four majors in one season.
However, Djokovic is now set for a major step up in the quality of opposition with Matteo Berrettini, the man he defeated in the Wimbledon final this year, his quarter-final opponent.
Djokovic vs Berrettini head-to-head
Djokovic wins: 3
Berrettini wins: 0
Berrettini is still a relative newcomer to the upper echelons of the ATP Tour, so it is little surprise they don't have a long history.
Djokovic has won all three of their meetings, with two of them coming at Grand Slams.
However, that doesn't tell the entire story. Firstly, Berrettini managed to take a set from the Serbian in each of the best-of-five matches, which shows he can hurt him.
They have also never played against each other on an outdoor hardcourt. How much of a difference that may make is unclear, as Djokovic is the greatest hardcourt player of all time. In theory, though, it is the surface best-suited to Berrettini's big-hitting power game too.
Novak Djokovic in focus
World ranking: 1
Turned pro: 2003
Career W/L: 976/197
US Open so far:
R1: Holger Rune 6-1, 6-7, 6-2, 6-1
R2: Tallon Griekspoor 6-2, 6-3, 6-2
R3: Kei Nishikori 6-7, 6-3, 6-3, 6-2
R4: Jenson Brooksby 1-6, 6-3, 6-2, 6-2
We predicted that Djokovic would drop a set to Brooksby in the last round and he did exactly that. The world No. 1 was forced to work hard by the young American, but the important thing was that he came through it.
The second set became a war of attrition, and that is the last thing you want to get involved in against Novak Djokovic.
There may be questions about how much the match took out of him physically, though. He is arguably the fittest player on the tour, but he is also 34 years old now and playing with increasing mental pressure every time he takes to court.
He is the favourite again, because he is Novak Djokovic, but he will be more aware than most of how tough a test this one could be.
Matteo Berrettini in focus
World ranking: 8
Turned pro: 2015
Career W/L: 108/59
US Open so far:
R1: Jeremy Chardy 7-6, 7-6, 6-3
R2: Corentin Moutet 7-6, 4-6, 6-4, 6-3
R3: Ilya Ivashka 6-7, 6-2, 6-4, 2-6, 6-3
R4: Oscar Otte 6-4, 3-6, 6-3, 6-2
The US Open is where Berrettini had his major breakthrough. The Italian went all the way to the semi-finals in 2019 before being eliminated by Rafael Nadal.
His game has been quietly developing since, and he has become a player with two major weapons: a huge serve and an even huger forehand.
The advantage of the serve may be negated by the fact he will be up against the best returner of all time in Djokovic, and the Serbian's defence will test the Italian's patience on the forehand too.
That said, Berrettini proved at Wimbledon he has what it takes to get to a Grand Slam final, and that should give him belief that he can do it again.
The downside is that Berrettini has not really fired on all cylinders yet at the US Open, but if he can find a groove then he is capable of beating anyone - including Djokovic.
Matteo Berrettini to win the first set 7-6
Djokovic has been a slow starter in his last two matches. He lost the opening sets against both Nishikori and Brooksby, so he has looked his most vulnerable early on.
Berrettini also won the first set against him in the Wimbledon final, so we know Djokovic can take a while to get the measure of the Italian.
The Italian has already been involved in a number of tie-breaks during the tournament, so watch out for him to win another on Wednesday.
Novak Djokovic to win 3-1
These two players have met twice before in Grand Slams and both times Djokovic has won 3-1.
There has been a similar pattern to both matches too, with Berrettini causing problems with his serve but Djokovic creating pressure with his defence and the Italian running out of patience.
Berrettini may have learned from those defeats, but if not then there is a very good chance this one follows the same pattern.
Matteo Berrettini to win 3-2
Berrettini should not be counted out of this one. He has enough talent, a big enough game to hit through even Djokovic's defence, and recent experience of doing very deep at a Major.
However, if he is to win it, the overwhelming likelihood is that he will have to go the distance.
That is a big ask - to essentially beat Djokovic over what would likely be four hours of tennis - but it may be the only way Berrettini can get it done.