Talk about a comeback. The 22-year-old Keys was ranked at No. 15.
There may only be one American ranked inside the world's Top 10 players, but four will take the court in the U.S. Open women's semifinals on Thursday night.
"I have had a very interesting year, surgery in the middle of it". If sone told me then I'd win the US Open, it's imposssible I'd say, absolutely impossible.
"I also have no idea how I have done it.just hard work".
The only thing that makes the loss more bearable for Keys is that if she had to lose to anyone, she would pick Stephens, just as she said.
Since then, she has racked up 14 wins in 16 matches, reaching the semi-finals in Toronto and Cincinnati before making a second career semi-final at the majors in NY.
"I'm honestly just honoured to be able to play at the same time as her, one of the greatest ever to play our game", Stephens, who joined spectators in clapping for Williams when she walked off the court, said.
At 37, Williams was attempting to become the oldest woman to win a Grand Slam title in the Open era.
Presented with the winner's check, Stephens said, 'That's a lot of money.
"Madison Keys will be her main rival but there are a lot of good players".
"Maddie is my best friend on tour", Stephens said.
"I know if it had been the other way round she would have supported me so that is what I am going to do for her. To stand her with today is incredible, that's what real friendship is".
Sloane Stephens watched January's Australian Open from her couch, a large cast on her left foot rendering her immobile and raising questions in her mind about her ability to bounce back from the injury.
Keys added: "Sloane is truly one of my favourite people and to get to play her was really special".
Stephens will jump to 17th in Monday's world rankings while Keys, who took home $1.825 million (€1.5 million) as runner-up, will rise to 12th. Madison Keys completed the clean quarterfinal sweep with a 6-3, 6-3 win over Kaia Kanepi on Wednesday.