The 19-year-old Gauff, now the youngest women’s finalist at the US Open since Serena Williams in 1999, triumphed 6-4 7-5 against Muchová and will face Aryna Sabalenka in Saturday’s showpiece.
The Belarusian mounted a superb comeback against American Madison Keys in Friday’s later game to win 0-6 7-6 (7-1) 7-6 (10-5).
Gauff, playing in front of a raucous home crowd, displayed composure and resilience against Muchová as she eventually wrapped up the contest on her sixth match point.
Prior to that, she came through a 40-shot rally – the longest of the tournament so far – to set up the decisive match point having failed to serve out for the win when she led 5-4 in the second set.
“It was a tough match,” Gauff told reporters. “I had leads, lost it, serving for it. It was a lot of emotional challenges in the match. But I think I did a good job of staying focused. I’m just really proud of myself today.”
Gauff quickly established a 5-1 lead in the first set before being pegged back by Muchová, this year’s defeated French Open finalist, with two breaks of serve.
But the American responded by winning the next game to love – her third break of the match – and taking the first set in 42 minutes.
A lengthy delay then ensued at the start of the second set after climate protestors in the crowd disrupted play.
Tournament organizers called it a “fan-related” incident inside Arthur Ashe Stadium and said that one attendee “affixed himself to the floor and due to the nature of this action, medical professionals, NYPD and security personnel were needed in order to resolve the issue and remove the fan from the stands.”
Both players left the court and the match eventually resumed following a 45-minute delay. Gauff seized the advantage after play resumed when she broke Muchová’s serve at 4-3 but needed to ride out a dramatic ending to the match.
She eventually sealed the win when a Muchová backhand drifted long, punching the air and roaring in delight.
Asked about her evolution since losing last year’s French Open final to Iga Świątek, Gauff said: “This time around, I have been focusing more on myself and my expectations of myself.
“Not going on social media or listening to people who believe that I can or believe that I can’t. I have just been really focusing on myself. I really believe that now I have the maturity and ability to do it. You know, regardless of what happens on Saturday, I’m really proud of how I have been handling the last few weeks.”
Sabalenka shows ‘fight’
Gauff’s next opponent, Australian Open champion Sabalenka, produced a monumental comeback against Keys in her semifinal, recovering from a set and a break down to win in a deciding 10-point tie-break.
Keys hit 12 winners as she bageled the Belarusian in the first set and held a 5-3 lead in the second set. But Sabalenka, who will soon be crowned No. 1 in the world after Świątek’s early exit at the tournament, hit back and played an excellent tie-break to level the match.
The 17th-seeded American once again took the lead with a break at 3-2 in the third set but Sabalenka stayed in touch with a break the following game.
After triumphing in the final-set tie-break, Sabalenka avoided a run of three-straight semifinal defeats at the US Open – and six semifinal exits from her last nine grand slam appearances.
“I was reminding myself that I lost a lot of tough matches,” Sabalenka told reporters. “I mean, one day all those matches should just help me somehow.
“This kind of thinking helped me to stay in the game and gave me some hope that I’ll be able to turn around this match, that the match is not over until the last point and that I just have to keep fighting, keep trying to find my rhythm, my game, just find myself.”
The US Open women’s singles final is set to take place on Saturday.