Serena Williams and Naomi Osaka will be hoping to secure a rematch of the 2018 US Open final when both semi-finals take centre stage on Thursday.
Japan's Osaka faces 25-year-old American 28th seed Jennifer Brady.
"I think she's a really amazing player, she has the variety that I wish I had so I'm a bit jealous," said 22-year-old Osaka.
Brady, the first female college player since Lori McNeil in 1987 to reach this stage, only won her first title last month. She also comes into this match having won 11 of her past 13 matches, never dropping a set in those victories
Osaka added: "She's super nice and I think it's going to be a really tough match and I think we're both going to try our best."
The Japanese player has improved as the tournament has progressed, with impressive victories over Estonian 14th seed Anett Kontaveit and then American Shelby Rogers in the quarter-finals.
Williams, similarly, has improved match by match and has noticeably grown stronger in the longer contests.
Her victory over Bulgarian Tsvetana Pironkova on Wednesday was her third successive three-set win at this tournament, and her second where she came from a set down.
"In the beginning I was a little bit fatigued for whatever reason so obviously I can't do that if I want to keep winning so I am going to try to figure that out," said Williams, who is seeking to equal Margaret Court's record of 24 Grand Slam singles titles.
She has faced her opponent Azarenka on 22 occasions, and won 18 of their meetings.
However, the Belarusian seems to be in peak condition. On Wednesday she showed glimpses of the form that led her to two Australian Open titles and the world number spot in the early 2010s during her 6-1 6-0 win over Elise Mertens.
"I'm so excited about this amazing opportunity to play a champion, someone I respect a lot and who's my friend," she said of her forthcoming semi-final. "I hope it will be fun - it'll be fun for me."
Osaka's match against Brady opens up the double bill at the Arthur Ashe Stadium at 00:00 BST before third seed Williams plays Azarenka.