The No. 6-seeded Djokovic, who won Wimbledon in July, had been drawn to face Federer with a semifinal berth at stake. Keys also lost to Stephens in the French Open semifinals this June.
Last year, all four women's semifinalists were Americans, and two of this year's are, Serena Williams and Madison Keys.
"He started very well", said Nishikori. Japanese for the third time in his career he reached the semi-finals on the Helmet, and each time before the turn Nishikori reached in NY.
Osaka, who is just 20 years old, is having a terrific 2018 season. She purported to be "freaking out inside", even if it certainly never showed.
But after labouring through the heat in her previous match, Tsurenko said she was sick Wednesday, waking up with a sore throat and not breathing well.
"Unfortunately during this tournament I had many issues with my health, and today was not my day obviously".
It was Osaka's, though.
She's the only member of that quartet who made it back to that round, using her big-strike game built on serves and forehands to overpower No. 30 Carla Suarez Navarro of Spain 6-4, 6-3.
"I believe that they kind of want to play the same, you know".
The Serb said that the trying conditions had made the match hard for both players.
She pushed some balls a few feet past the baseline, often failing to make Osaka do anything special to win a point and finishing with 31 unforced errors.More news: Samsung Rumoured To Be Launching Quad-Camera Smartphone This Year
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"I came out in the match great, 6-2, 4-2 serving, and everything was going great", said Cilic.
Kei Nishikori got some measure of revenge Wednesday at the US Open against Marin Cilic.
After being involved in a five-setter of his own less than 24 hours on, Cilic was asked if he caught any of Nadal and Thiem's thrilling battle.
He had a letdown at the very end, too, rallying from 4-1 down to 4-all, before Nishikori grabbed the last two games.
It has already been a successful return to Flushing Meadows for Nishikori, who missed the US Open past year with a wrist injury that saw his ranking plunge and put him on the comeback trail that included playing Challenger-level tournaments.
Ironically, the last time Nishikori beat Djokovic was in the semi-finals of the US Open, back in 2014.
Millman, who had performed a major turnaround by knocking out Swiss tennis maestro Roger Federer from the tournament, suffered a crushing 3-6, 4-6, 4-6 defeat at the hands of his Serbian opponent to storm into the semi-finals.
The victory for Nishikori means that for the first time in the open era there will be a Japanese man and woman contesting the semifinals of a grand slam as Naomi Osaka cruised past Ukraine's Lesia Tsurenko 6-1 6-1.
The victor of this match will face the either the world no. 1 Rafael Nadal or the 2009 US Open champion Juan Martin Del Potro in the Sunday final. "Just a little bit of a shift of the momentum there".
How tense and tight was this one?
Those in Djokovic's box were seen looking around as if they were trying to find whatever Nole was requesting.