|Venue: Flushing Meadows, New York Dates: 28 Aug-10 Sept|
|BBC coverage: Live radio and text commentary on selected matches every day.|
Unseeded Sloane Stephens held her nerve to beat Venus Williams in three sets and set up a US Open final against fellow American Madison Keys.
Stephens, ranked 83rd after recently returning from injury, won 6-1 0-6 7-5 in the first semi-final at Flushing Meadows in New York.
In another all-US contest, 15th seed Keys then beat Coco Vandeweghe, seeded 20th, 6-1 6-2.
Both Stephens and Keys will make their Grand Slam final debuts on Saturday.
It will be the first time since Serena Williams beat Venus in 2002 that a US Open women’s final has featured two American players.
“Having four Americans in the semi-finals, I think that says a lot about American tennis and where we are right now,” said Stephens.
“I don’t think I would have had it any other way. I’m just super proud and honoured to be a part of what these four girls were, what we did tonight.”
- Watch: 5 live commentary team look ahead to the final
- Keys thrashes Vandeweghe to make final
- Live scores and results
Stephens only returned to action at Wimbledon, ranked 957th, after missing 11 months with a foot injury.
Two months later the 24-year-old is on a run of 14 wins in 16 matches and through to her first major final, with her speed of foot and athleticism to the fore.
“I have no words to describe my feelings and what it took to get here. I have no words,” said Stephens.
“I have no idea how I have done it. Your guess is as good as mine.
“If someone had told me when I started my comeback that I would make two semi-finals and a Grand Slam final I would have passed out. I don’t know how I did it. Just hard work.”
Williams, 37, misses out on returning to the US Open final 15 years after her last, and the two-time champion will end 2017 without adding another major title despite reaching two finals and a semi-final.
“For me, it’s about putting myself in the position all the time to get the titles, and that’s exactly what I did,” said Williams.
“That’s all I could do.”
‘I hung tough, gritted it out’
Williams was playing in her 23rd major semi-final, as opposed to Stephens in her first, but the seven-time Grand Slam champion made a nervous start.
Seventeen unforced errors from Williams saw the first set disappear in 24 minutes, and she was in danger again facing three break points at the start of the second.
However, she grew in confidence from clinging on and began to attack the Stephens serve at will, breaking three times to level without dropping a game.
After 54 minutes of wildly uneven quality, the third set proved to be a gripping decider.
Williams twice recovered from a break down and appeared to be on the brink of victory at 5-5, 30-30, pushing Stephens back into the corner as she advanced to the net.
It brought the best out of the younger player, who found a magnificent backhand pass that brought the 23,000 spectators to their feet and wrenched the initiative her way.
Stephens would win six points in a row, including chasing down two drop shots and making spectacular winners, on her way to breaking the Williams serve.
Both women had dropped serve five times, but there was no wobble from Stephens as she moved confidently to match point, before Williams tamely netted a return.
“I hung tough, gritted it out,” said Stephens. “I worked my tail off. We played some incredible points in the third set.”
BBC Sport tennis correspondent Russell Fuller
After two of the most one-sided sets you are ever likely to see in a Grand Slam semi-final, Williams threw everything she had at Stephens in the decider.
The younger American’s defence was extraordinary, but it was matched by the resilience of Williams who twice recovered a break.
And then, as she served to stay in the match, at 4-5 30-all, Stephens hit one of the backhand winners of her life to end a pulsating rally – and went on to win 10 of the last 11 points.
She was ranked 957 in the world in late July, after nearly a year out with a foot injury.
“Eventually, I will beat someone,” she said after a first-round defeat in Washington the following week.
How right she was.
|Follow tennis with the BBC|
|Alerts: Tennis news sent to your phone|
|My Sport: Sign up to follow tennis news|