Aryna Sabalenka fought back from the brink of defeat to overcome American 17th seed Madison Keys in a third-set tie-break and line up a US Open final against home favourite Coco Gauff.

Keys served for the match in the second set but incoming world number one Sabalenka overhauled the 2017 runner-up to win 0-6, 7-6 (7/1), 7-6 (10/5) to reach her second Grand Slam final.

"I'm really proud of myself that I was able to turn around this game and get this win, because it was just incredible," said Sabalenka.

"I was just, like, 'Come on, keep trying, keep pushing, like, I don't know, do something extra. Just try to turn around this match.'"

"It really means a lot to be in the final of the US Open for the first time," she added.

Keys was left devastated by the loss after going agonisingly close to a second Grand Slam final.

"I think everyone at the start of the tournament would obviously be really, really excited to be in the semis. Right now it sucks," said Keys.

"But yeah, I just think being able to, you know, take this and turn it to a positive is really possible. Yeah, there is still a lot to be proud of and still tons of tennis to play this season."

Sabalenka rode an emotional rollercoaster, angrily remonstrating with her coaching team at times, before being able to sheepishly laugh off celebrating prematurely in the decisive tie-break.

"I thought that we play tie-break up till seven. I was just all over the place," she said.

"I was thinking that if I'm going to lose this semi-final, I'll be struggling with sleeping for I don't know how many days, and I was just, like, I don't want this to happen. I need some sleep."

The Australian Open champion will bid for her second Grand Slam title on Saturday against the 19-year-old Gauff. The American holds a 3-2 edge but this will be their first meeting at a major.

"She's an unbelievable player," said Sabalenka. "The crowd will be supporting her a lot. I will do everything I can. I'll be fighting for every point and I will do my best."

- Sabalenka's nightmare start -

Sabalenka beat Keys in straight sets in the Wimbledon quarter-finals but was pushed to her limit by an opponent who knocked out two top-10 players en route to the last four in New York.

The second seed handed Keys a break in the first game with a double fault and her troubles were compounded when she again dropped serve after leading 40-0 two games later.

Keys shook off two break chances before a wayward Sabalenka faltered on serve for a third time, allowing her opponent to wrap up the set with ease.

Sabalenka raised her arms in mock celebration as she held to finally get on the board to start the second set.

Keys continued to pump winners with her powerful forehand and broke again for a 2-1 lead, Sabalenka drawing a code violation after smacking a courtside barrier and hurling her racquet towards her coach.

The Belarusian briefly got back on serve before Keys struck once more, further infuriating an irate Sabalenka who had stormed into the semi-finals without losing a single set.

Sabalenka broke Keys to love to stay in the tournament, winning 12 points in a row to move 6-5 ahead, but she couldn't convert two set points as the American steadied herself to force a tie-break.

However Sabalenka won that easily to send the match to a deciding set, before which Keys took a medical timeout to receive treatment to her upper left leg.

Keys withstood an early break point and the first five games went on serve before a loose game from Sabalenka handed Keys the initiative at 4-2.

Sabalenka dug deep and overpowered Keys to retrieve the break straight away, surviving two more break points to level at 4-4.

The Belarusian took charge in the tie-break, leading from the front before securing a second win over Keys in as many Grand Slams.