Here are some of the celebrities who attended Day 8 matches.
Mirka & Anna Wintour - Roger Federer #1 fans
Robert Federer & Gavin Rossdale - Also Roger Federer's #1 fans
Rob Thomas and wifeAnd speaking about celebrities, Novak Djokovic is a star of his own.
He has impersonated Maria Sharapova, Rafael Nadal and others in the past.
Last night, Djokovic added to his repertoire of memorable impersonations by channeling his inner John McEnroe in front of the majority-American crowd.
Check out the video here by tennisnakama.
Earlier Djokovic defeated Radek Stepanek 6-1, 6-3, 6-3.
There was another thing for the American crowd to cheer about last night.
America's newest darling, Melanie Oudin, continued her dream run at the US Open with another upset over Russian Nadia Petrova.
The teenager won 1-6, 7-6, 6-3.
The biggest upset of the day has to be Caroline Wozniacki who sent off Svetlana Kuznetsova.
The Danish teen toppled the former US Open champ 2-6, 7-6, 7-6 to reach her first grand slam quarterfinal.
American John Isner’s 4-6, 6-4, 6-4, 6-4 defeat to Fernando Verdasco marked the first time since 1968 that no American men's players advanced to the US Open quarterfinals.
Here's the rest of the results:
US Open men's singles fourth-round results from New York on Tuesday (prefix denotes seeding)
4-Novak Djokovic (Serbia) beat 15-Radek Stepanek (Czech Republic) 6-1 6-3 6-3
10-Fernando Verdasco (Spain) beat John Isner (US) 4-6 6-4 6-4 6-4
1-Roger Federer (Switzerland) beat 14-Tommy Robredo (Spain) 7-5 6-2 6-2
12-Robin Soderling (Sweden) beat 8-Nikolay Davydenko (Russia) 7-5 3-6 6-2 (Davydenko retired)
US Open women's singles fourth-round results from New York on Tuesday (prefix denotes seeding)
9-Caroline Wozniacki (Denmark) beat 6-Svetlana Kuznetsova (Russia) 2-6 7-6(5) 7-6(3)
Yanina Wickmayer (Belgium) beat Petra Kvitova (Czech Republic) 4-6 6-4 7-5
Melanie Oudin (US) beat 13-Nadia Petrova (Russia) 1-6 7-6 (2) 6-3
Kateryna Bondarenko (Ukraine) beat Gisela Dulko (Argentina) 6-0 6-0
(Via AP, Reuters, TVNZ, US Open website)