NEW YORK — Both US Open finals this weekend will feature an American after Jessica Pegula fought back to beat Karolina Muchova 1-6, 6-4, 6-2.

Down a set and a break, the idea that Pegula would boost interest in the women’s tournament felt fanciful, but she showed great courage in turning the match around against an opponent who was eventually exhausted. Muchova had only just returned from a nearly 10-month absence with a wrist injury and had suffered from stomach problems during her previous-round win over Beatriz Haddad Maia.

On Saturday, second-seeded Aryna Sabalenka will face Pegula, who earlier in the evening eliminated fellow American semifinalist Emma Navarro. With either Frances Tiafoe or Taylor Fritz in Sunday’s men’s final, it promises to be a banner weekend for American tennis and a chance for Pegula to fulfill a lifelong dream at age 30.

Jessica Pegula is in her first Grand Slam final. (Luke Hales/Getty Images)

She could smile in disbelief at that prospect at the end of the match, but the jubilant scenes that followed the final point felt a long way off at the start. The atmosphere in Arthur Ashe Stadium was flat during the opening exchanges. Many of the fans in attendance were likely reeling from the excitement at the end of Sabalenka’s win over Navarro in the first semifinal, and the more subdued mood suited Muchova better than Pegula.

The Czech was able to display her unparalleled variety without having to worry about external factors, and Pegula also seemed flat, perhaps still feeling the effects of her victory over Iga Swiatek 24 hours earlier.

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After clearing three break points in the third game, Muchova took control of the first set, thanks in large part to her devastating volleying, rarely seen on the WTA Tour. The same goes for the slice, which Muchova employed with similar success. As she ran along the baseline, Pegula was required to hit the ball, and there was the waiting Muchova, ready to tap away a volley.

To underscore the contrast between the two players, Pegula tried a similar tactic late on. Except when she did, she hit her volley from a difficult position and the ball landed in the bottom of the net, giving Muchova a 5-1 lead. Five points later, the set was over in less than 30 minutes. “She made me look like a beginner, I was on the verge of tears,” Pegula said on court after her victory.

Karolina Muchova defeated Jessica Pegula in the first set. (Charly Triballeau / AFP via Getty Images)

This was what Pegula must have feared. When she is confident, Muchova enters a kind of flow state where everything seems effortless. Emboldened by a decisive lead, she can run through her full repertoire of strokes. A drop shot helped her to a break in the first game of the second set, and she jumped to the chair to switch sides.

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Pegula trudged on. This was getting uncomfortable. Her victory over Swiatek was her first in a Grand Slam quarterfinal in her seventh attempt, but this training didn’t feel like a real reward.

Even when Muchova missed a shot, she seemed excited to try again on the next point — like an inventor constantly coming up with new ideas. She looked like she was in batting practice; Pegula looked like she was in a bad dream.

Jessica Pegula struggled to get into the match until the fourth game of the second set. (Scott Wenig / Associated Press)

The No. 6 was in dire need of a moment to get herself and the crowd going. That came in the third game of the set, when, with break point looming, she attempted a forehand slice and did enough with it to draw a missed volley from her opponent.

“That was luck,” she said afterwards.

Pegula then held on and scored 2-1. He broke Muchova’s serve for the first time in the next game, defended well again and could finally enjoy himself when the Czech was at the net.

In the next game, Muchova faced another break point and Pegula, thanks mainly to her willpower, won three games in a row to take a 3-2 lead.

Whether Muchova was hung up on that missed volley for 3-0, or was suffering from a lack of match fitness so early in her comeback from wrist surgery, her level dropped just as Pegula was raising hers. Pegula broke again, thanks to a brilliant inside-in forehand winner and then a clean strike on the backhand side. She also found much more depth in her lobs, forcing Muchova to hit increasingly difficult smashes. Pegula even hit one over Muchova’s head and onto the baseline in the next game.

Muchova won seven out of seven points in the first set; in the second set she only won 11 out of 19.

Although Pegula was broken back immediately, Muchova’s rhythm was gone. She was no longer fluid, her strokes suddenly weren’t as natural. Pegula felt it and started to improve her returns. After a double fault when she was down 5-4 on set point, Muchova immediately left the court. It was the first set she lost the entire tournament.

Early signs in the third set were not encouraging for her. Muchova was spraying forehands and it felt like the match was now Pegula’s to lose. She held serve to take the lead on the scoreboard for the first time in the match and then broke for 2-0. Muchova, perhaps wary of Pegula’s improved defense, perhaps feeling physically unfit, made fewer darts to the net. That was good news for the American, who fended off a break point and held on for 3-0.

Jessica Pegula turned a losing match around as Karolina Muchova’s level dropped. (Sarah Stier/Getty Images)

Muchova could have given up at this point, but she showed an enormously impressive determination to keep fighting. She trailed 3-1, 40-30 and produced two of the most astonishing defensive points ever seen on this court. The second ended with a flicked one-handed backhand pass, which set up a break point.

When Pegula saved that point, it felt like an important battle had been won.

Ditto the American’s next service game, which she won on the sixth attempt after a series of tense exchanges. The crowd was now really into it, roaring their encouragement as Pegula went on to take a game of the final. Muchova, meanwhile, showed that she even expresses her frustration in artistic ways, throwing her racket high into the New York night and catching it like a circus performer.

Two tiring errors from Muchova, a missed overhead and another slice — the hallmarks of her electrifying first set — heralded the beginning of the end. At 0-40, on a second serve, Muchova stole a point, but another slice went wide and Pegula’s arms were up.

After breaking her personal quarter-final ceiling on Wednesday night, a place in the history books could await her on Saturday.

(Top photo: Luke Hales/Getty Images)