Three of the top four seeds in the men's singles bracket advanced to the semifinals of the 2021 U.S. Open. 

No. 1 seed Novak Djokovic faces off against No. 4 seed Alexander Zverev. No. 2 seed Daniil Medvedev clashes with 12th-seeded Canadian Felix Auger-Aliassime. 

Djokovic will be under the most pressure of the four semifinalists since he is chasing the calendar Grand Slam. He went through the toughest test of the final eight in his four-set win over Matteo Berrettini. 

Medvedev, Auger-Aliassime and Zverev should all be well rested ahead of Friday's semifinals. 

Medvedev has had the longest layoff after his win on Tuesday afternoon, Auger-Aliassime played a set-and-a-half in the last round and Zverev went to four sets once in his first five matches. 

The U.S. Open men's semifinals begin at 3 p.m. ET on Friday. Both matches can be viewed on ESPN. The contests can be live-streamed on the ESPN app and ESPN.com.

No. 1 Novak Djokovic vs. No. 4 Alexander Zverev

One of the two matchups everyone wants to see in the men's singles bracket will take place on Friday. The other is a potential final between Djokovic and Medvedev. 

Djokovic won each of the season's first three majors, but Zverev beat the No. 1 player in the world in Tokyo on his way to the Olympic gold medal. 

Zverev carries a 16-match winning streak into the semifinal showdown. 

The fourth-seeded German is in the best possible spot to pull off another upset of Djokovic. He is in great form and playing with a ton of confidence, and he went through an easy quarterfinal match against Lloyd Harris. 

Zverev took a set off Djokovic in the Australian Open quarterfinals to start the season, and he played very well against him in Tokyo after dropping a set. 

Djokovic could be viewed as vulnerable because of the three-hour battle he went through on Wednesday night versus Berrettini.

The No. 1 seed prevailed after losing the first set, but the showdown with the No. 6 seed was physically draining. The first set alone lasted more than an hour.

Djokovic is also facing the shortest turnaround time between the quarterfinals and semifinals. That may not be a major factor for the top player in the world, but it certainly is not an ideal situation for him to face. 

Zverev could take a set or two off Djokovic on Friday night, but he needs to turn in a perfect performance, like he did in Tokyo, to end his run at the season-long Grand Slam. 

No. 2 Daniil Medvedev vs. No. 12 Felix Auger-Aliassime

Medvedev and Auger-Aliassime should be more than fresh for their Friday showdown.

The second-seeded Russian labored through more time on the court than his Canadian foe on Tuesday, but he was the first player to qualify for the semifinal round. 

Medvedev will have two full days of recovery under his legs, and that could be massive as he tries to fight off the threat from Auger-Aliassime.

The No. 12 seed played a pair of four-set matches and one five-setter in the first four rounds. The second-set retirement of Carlos Alcaraz in the quarters will have aided Auger-Aliassime's ability to put up a challenge against Medvedev. 

Medvedev carries a significant edge in experience. He has been to three Grand Slam semifinals, all of which have been at hard-court majors. 

Both of Medvedev's semifinal victories came in straight sets. He beat Grigor Dimitrov at the 2019 U.S. Open and Stefanos Tsitsipas at the 2021 Australian Open.

Medvedev has won all but one set in New York over the last week-and-a-half. The one concession occurred in the third set against Botic van de Zandschulp on Tuesday. 

Auger-Aliassime took a set off Medvedev in their lone head-to-head meeting, but that came back in 2018 before the Russian took the next step on the Grand Slam stage. 

The Canadian has played well in New York, but Medvedev can be difficult to beat on hard courts when he is at his best, and that should come shine through on Friday.