The U.S. Open women’s final is perhaps the most surprising Grand Slam final in tennis history, featuring two unseeded teenagers, including the first qualifier to play in a final in the Open era.

Leylah Fernandez will face Emma Raducanu, and the teenagers — Fernandez turned 19 this week, and Raducanu is 18 — have been the sensations of a U.S. Open that began without many of the most significant stars in tennis. Roger Federer, Rafael Nadal and Serena and Venus Williams were forced to skip the tournament with injuries. Fernandez, of Canada, and Raducanu, of Britain, have more than filled the void. Their tennis and infectious personalities have been nothing short of show stopping.

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Raducanu took the long way, quickly.

Ranked 150th, Raducanu had to play in the qualifying rounds of the U.S. Open a week before the main-draw tournament began, in order to secure her spot. Raducanu won three matches to reach the main draw, and then six more matches to reach the final, becoming the first player in history to reach a major final as a qualifier.

While many players would look haggard after nine matches in one tournament, Raducanu looks hale and happy, helped by her incredible efficiency on court. Raducanu has won all nine of her matches in straight sets, never needing so much as a tiebreaker in any of the 18 sets. In only one set, in the second round of qualifying against Mariam Bolkvadze, did her opponent reach five games. Bolkvadze led with Raducanu serving at 4-5, 0-30, two points from taking the second set, only for Raducanu to reel off 12 straight points to end the match.

Remarkably, despite playing three more matches, Raducanu has spent less time on court than Fernandez at this U.S. Open, totaling 11 hours and 34 minutes in nine matches, compared with Fernandez’s 12 hours and 45 minutes in six matches.

Fernandez is a giant killer.

While Raducanu has rolled, Fernandez has fought, beating some of the game’s toughest players in three-set battles. After winning her first two matches against the past quarterfinalists Ana Konjuh and Kaia Kanepi, Fernandez knocked out the defending champion, Naomi Osaka, in three sets in the third round. The third-seeded Osaka served for the match at 6-5 in the second set, but Fernandez broke and ran away with the second-set tiebreaker as Osaka unraveled.

In the fourth round, Fernandez beat Angelique Kerber, the 2016 U.S. Open champion, in three sets. In the quarterfinals, Fernandez beat the fifth-seeded Elina Svitolina in a third-set tiebreaker. In the semifinals, Fernandez beat the second-seeded Aryna Sabalenka in three sets.

“It has helped me open my eyes that I have no limit to my potential,” Fernandez said of her run. “I can go three sets against these players, I can play against these top players, and I can win against these top players.”

Though Fernandez has paid a higher physical toll to reach the final, she will enter it far more battle tested. She has proved what she can do deep into a third set of an important match, while Raducanu’s response in those situations remains largely unknown.