NEW YORK — Coco Gauff never wavered one bit Thursday night. Not when match point after match point went by the wayside. Not during a 40-shot exchange that ultimately helped decide the outcome. And not, most distracting of all, when her U.S. Open semifinal against Karolina Muchova was interrupted for 50 minutes by environmental activists — one of whom glued his bare feet to the concrete floor in the stands.

It’s been rather obvious for quite some time that Gauff is no ordinary teenager. Now she is one win away from becoming a Grand Slam champion.

Gauff, a 19-year-old from Florida, reached her first final at Flushing Meadows by defeating Muchova 6-4, 7-5 on what was anything but an ordinary evening.

“I really believe that now I have the maturity and ability to do it,” said Gauff, who came close to a major trophy last year in the French Open but lost the title match. “You know, regardless of what happens on Saturday, I’m really proud of how I have been handling the last few weeks.”

The No. 6-seeded Gauff will meet No. 2 Aryna Sabalenka of Belarus for the championship Saturday. Sabalenka beat 2017 U.S. Open runner-up Madison Keys 0-6, 7-6 (1), 7-6 (10-5) in a topsy-turvy second semifinal that finished at nearly 1 a.m.

Sabalenka won the Australian Open in January, is 23-2 in Grand Slam matches this season and is guaranteed to move up to No. 1 in the world for the first time next week. She was on the verge of losing to Keys, who was up 5-3 in the second set, but used a 12-point run to get back into the match.

Tiebreakers at 6-all in the third sets of women’s Grand Slam matches now are first-to-10 — unlike the old first-to-seven setup — but Sabalenka clearly forgot that. When she moved out front 7-3, she dropped her racket and put her hands to her face, covering a huge smile. Then Sabalenka quickly realized there was work to be done and finished the job on her third match point.

“I was all over the place,” said Sabalenka, who was able to laugh about her mistake afterward.

The toughest part against Muchova for Gauff might have been closing out the victory: She needed six match points to get it done, raucously supported by a loud, partisan crowd that chair umpire Alison Hughes repeatedly implored to quiet down.

After failing to convert one match point while serving for the win at 5-3, then another four in what turned out to be the last game, Gauff got the last chance she would need when she smacked a forehand winner to cap that 40-swing point that was the longest of the contest.

“I knew I had the legs and the lungs to outlast her in the rally; it was whether I had the mentality and patience to do it,” Gauff said. “After 10 or 15 shots in, I was, like, ‘Well, this is going to change the match.’”

Sure did.

On the next point, Muchova missed a backhand, and it was over. Gauff pumped her fists, waved to the fans and put a finger to her ear, as if to say she wanted to hear even more support.

She is the first American teenager to make it to the title match in New York since Serena Williams, one of her idols, then quoted another, the late NBA star Kobe Bryant, by telling the fans: “Job’s not done.”

Gauff was up by a set and 1-0 in the second when four climate protesters disrupted play from seats in an upper level of the arena. All four were arrested; three were escorted away relatively quickly, but it took more time to remove the person glued to the ground.

“If that’s what they felt they needed to do to get their voices heard,” Gauff said, “I can’t really get upset at it.”

Both women spent time in the locker room during the delay. When action resumed, the play was pretty even for several games, until Gauff surged ahead and got her first match point. Muchova erased that with a volley winner and broke back.

They would play on for nearly a half-hour.

With Gauff leading 6-5 and Muchova serving, the one-point-away count kept climbing. Muchova resisted. Gauff was unable to pull through.

11 Straight Wins for Gauff

Once. Twice. Three times. Four. The roars from the seats kept coming. Finally, Gauff completed her 11th win a row and the 17th in her past 18 matches, a run that began after a first-round exit at Wimbledon in July. The streak includes the two biggest titles of Gauff’s career — and now she needs one more win to get an even more important championship.

“After Wimbledon, I wasn’t expecting to do well, honestly, in this hard-court season,” Gauff said, “so I’m really proud of the way I have been able to turn this season around for me.”

When Gauff and Muchova got started at 7:15 p.m., it was cloudy and considerably cooler than it’s been this week at Flushing Meadows, dropping from nearly 95 degrees Fahrenheit (35 Celsius) on Wednesday to the low 80s F (high 20s C).

Gauff was terrific at the outset, racing to leads of 3-0 and 5-1 before No. 10 seed Muchova, a 27-year-old from the Czech Republic, finally got going. By the end, though, Muchova had won the point on just 10 of her 24 trips to the net and she had accumulated 36 unforced errors, 11 more than Gauff.

“Just kind of sad about the performance,” said Muchova, who reached the final at Roland Garros in June.

She was visited by a physiotherapist during the extended break caused by the protest and said her right arm — covered by a black sleeve — bothered her during the tournament.

If she wasn’t at 100% — what player is by this point of the season? — Gauff deserved credit for finding the right times to let Muchova miss as opposed to trying to get too aggressive.

“You have to be focused and finish points,” Muchova said about facing Gauff. “You have to be there on the court and then see where she is running. You have to think where to put the ball to finish it at the net or try to play it earlier.”

What Gauff also displayed was that she was ready for the moment, the sort of success predicted of her since, at age 15 in 2019, she became the youngest qualifier in Wimbledon history and got to the fourth round there.

“I’m having way more fun now,” Gauff said Thursday.

Men’s Semifinals Are Tonight

No. 2 seed Novak Djokovic considers his mental state just as important as his physical condition when it comes to being prepared to play his best at age 36.

“Mentally there is probably a lot more that I’m dealing with in my private life than was the case 10 years ago. But that’s the beauty of life. Things are evolving, moving on,” said Djokovic, who will try to take another step toward what would be a 24th Grand Slam title when he faces unseeded American Ben Shelton in the U.S. Open semifinals on Friday.

“I just feel that there is always, I guess, an extra gear that you have inside of you and you can find when you dig deep to handle and manage energy levels, on and off the court,” Djokovic said, “if you’re really devoted to that and if you care about it, if you pay attention to that mental aspect as much as physical, of course.”

On the other side of the bracket, top-seeded Carlos Alcaraz of Spain takes on 12-seeded Alexander Zverev of Germany.