US OpenVenue: Flushing Meadows, New York Dates: 28 Aug-10 SeptBBC coverage: Live radio and text commentary on selected matches every day.
Two all-American semi-finals will take place on day 11 of the US Open as Venus Williams plays Sloane Stephens and Coco Vandeweghe faces Madison Keys.
It is the first all-US last four line-up at the tournament since 1981.
Williams, the 2000 and 2001 champion, and Stephens will be first on the Arthur Ashe Stadium in New York at 00:00 BST.
Vandeweghe, seeded 20th, 15th seed Keys and unseeded Stephens are aiming to reach their first Grand Slam final.
• Keys sees off Kanepi in straight sets
• Vandeweghe beats Pliskova to make semis
• Kvitova's 'amazing' return to the court
Williams and Stephens both won final-set tie-breaks to reach this stage, against Petra Kvitova and Anastasija Sevastova respectively.
Vandeweghe overcame Karolina Pliskova in straight sets to join them, while Keys saw off unseeded Estonian Kaia Kanepi.
'Venus is our leader'
Ninth seed Williams, 37, is the oldest semi-finalist at any Grand Slam since Martina Navratilova at Wimbledon in 1994.
"It's such a wonderful feeling, because you put in so much work to be able to succeed at these moments," said Williams.
"It has been a great two weeks for American tennis, seeing all the American players in the draw and all of them advancing so deep and competing so well."
Stephens, 24, added: "Making the semi-finals of a Slam is a complete neutraliser, anybody's game. I just have to focus on myself.
"Venus is just our leader, everyone looks up to her. She's a great player, a great person. She's a great leader."
Arthur Ashe became the first black man to win a Grand Slam when he triumphed at the 1968 US Open and Williams and Stephens will face each other on the court named after the three-time major winner.
"It's great for American tennis," said Stephens. "It's great for African-American women. I hope that we keep it going."
Williams, who reached the final at her first US Open in 1997, the same year the Arthur Ashe Stadium made its debut, added: "He's a total legend.
"He played during a time where he couldn't just focus on the tennis. I'm very blessed to be able to focus on my game. But he had to fight because of the colour of his skin.
"It was a completely different time. So I can't even imagine the pressure he was under. To come out of it with grace, as a champion, it's incredible."
Vandeweghe's 'Jedi mind tricks'
Vandeweghe was the third American to reach the semi-finals after she saw off world number one Pliskova 7-6 (7-4) 6-3, knocking the Czech off the top of the rankings at the same time.
It is the first time the 25-year-old, who won the junior championship at Flushing Meadows as a 16-year-old in 2008, has reached this stage of the US Open.
Vandeweghe recently began working with Pat Cash and credits the 1984 men's singles semi-finalist with helping her to keep calm on court.
"Maybe it's like some Jedi mind trick," said the 20th seed.
"I think the biggest thing is channelling my intensity and tenacity out onto the court and putting it into a singular focus. I think that's probably one of the biggest things he's implemented into my regimen."
Keys completed an all-American final four for the first time in 36 years. Tracy Austin - who would go on to be champion - Chris Evert, Martina Navratilova and Barbara Potter were the last US quartet in the semi-finals.
The 15th seed beat former world number 15 Kanepi 6-3 6-3 in only one hour and eight minutes.
Keys, 22, is bidding to reach a first Grand Slam final with her run at Flushing Meadows this year matching her best performance in a major, when she reached the Australian Open semi-final two years ago.
"I have been taking this whole tournament one match at a time, one point at a time," said Keys.
"I'm definitely not getting ahead of myself in that way.
"I'm really proud of getting here in the first place. I'm just going to keep focusing on the next match and then breaking it down from there."
British pair into men's semi-final
Meanwhile in the men's wheelchair doubles, Britain's Alfie Hewett and Gordon Reid, who retained their Wimbledon title in July, have made it through to the semi-finals.
The second seeds will face the unseeded pair of Gustavo Fernandez of Argentina and Japan's Shingo Kunieda.
In the women's wheelchair doubles, Britain's Lucy Shuker and partner Yui Kamiji of Japan will take on USA's Dana Mathewson and Aniek Van Koot of the Netherlands in the semis.