Sloanes triumphed 6-1 0-6 7-5 to seal her spot in Saturday's final at Flushing Meadows
Sloane Stephens will face Madison Keys in the US Open final as the next generation of American talent took centre stage at Flushing Meadows.
After two decades of dominance from the Williams sisters, either 24-year-old Stephens or 22-year-old Keys will become the first American woman from outside the family to win a grand slam singles title since Jennifer Capriati in 2002.
Venus Williams led four players from the host nation into the semi-finals for the first time in 36 years and boasted more wins in New York than the other three put together.
But the 37-year-old had to cede the advantage to Stephens, who prevailed in a terrific deciding set to win 6-1 0-6 7-5 before Keys crushed Coco Vandeweghe 6-1 6-2.
Both young women might well have expected the US Open to come too soon after injury problems this season.
Stephens' comeback has been the more dramatic. The former Australian Open semi-finalist was unable to walk after foot surgery in January and was playing in just her fifth tournament since returning from injury.
She was ranked down at 934 only a month ago, and said: "I have no words to describe what I'm feeling, what it took to get here, just the journey I've been on, I have no words.
"When I started my comeback, if somebody told me I was going to make two semis and a grand slam final, I would probably have passed out, which is what I feel like right now. I don't know how I got here, just hard work, that's it."
Keys has struggled with pain in her wrist and has twice been under the knife, most recently after the French Open in June.
The 22-year-old has long been touted as a future slam champion and showed why here, giving good friend Vandeweghe little chance in a performance that saw her hit 25 winners and only nine unforced errors.
Keys was 5-0 up after 13 minutes having allowed Vandeweghe only four points and, although it became a little more competitive from there, the result never looked in doubt.
The only concern for Keys was a medical time-out she took late in the match, returning to the court with strapping on her right thigh.
She said: "I'm still shaking. I think I played pretty well tonight. I knew I had to rise to the occasion and I'm just really happy to be in the final. I couldn't feel better than I feel right now.
"Sloane is a new person right now, she's really loving being out on the court again and she's obviously playing really well. I'm really excited we get to play each other in a US Open final. It's pretty cool to say."
The first semi-final turned into a tremendous battle after two one-sided sets, the first dominated by Stephens and the second by Williams.
Stephens returned from her 10-month break with a new, relaxed attitude, happy simply to be playing tennis again.
And that showed in the final stages as she held her nerve superbly against a player who first made the US Open final 20 years ago.
Williams was two points away at 5-4 30-30 but Stephens won a jaw-dropping rally with a backhand winner down the line and did not look back.
"That was good," she said. "And the next game I played, incredible. I think that really gave me some momentum and really pumped me up. When you get your chance, you've really just got to take it and make the most of it."
It was another case of so near and yet so far this year for the evergreen Williams, who was beaten in the final of both the Australian Open and Wimbledon nine years after her last grand slam title.
She said: "It was definitely well competed. She ended up winning more points than I did. I continued to play aggressive and continued to play the kind of match that it takes to win. Just made too many errors there at the end.
"For me, it's about putting myself in the position all the time to get the titles, and that's exactly what I did. That's all I could do."
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