Emma Navarro, one of two American women to make the second week at Wimbledon, was eliminated by No. 7 seed Mirra Andreeva 6-2, 6-3 in the fourth round Monday.
Andreeva, an 18-year-old Russian, was one of 11 teenagers in the men's and women's main draws at Wimbledon, and was the only one to advance to the round of 16.
She was also the last person on Centre Court to realize she had won Monday, so focused on not thinking about the score that she didn't grasp that the match was over when Navarro netted a forehand.
So instead of celebrating, Andreeva calmly turned back toward her baseline and then started fiddling with her racket, seemingly getting ready for the next point.
It wasn't until she noticed the reaction from the crowd -- and coach Conchita Martinez celebrating -- that it dawned on her that she had won.
"Honestly, I just kept telling myself that I'm facing break points. I tried to tell myself that I'm not the one who is up on the score, I'm the one who is down," Andreeva said in an on-court interview. "In the end I completely forgot the score. I'm happy that I did it because I think that [otherwise] I would be three times more nervous on the match point."
With the win, Andreeva became the youngest player since Nicole Vaidisova in 2007 to reach the women's quarterfinals at the grass-court Grand Slam tournament.
Maria Sharapova at 17 was the last teenage player (men's or women's) to win the Wimbledon title.
The score wasn't the only thing that Andreeva tried to ignore. She was also afraid to look up at the Royal Box, where eight-time men's Wimbledon champion Roger Federer was watching the match together with his wife, Mirka.
"I really tried my best not to look over there in the box, because I knew that as soon as I would look there I would just completely lose my focus," she said, before addressing the couple directly. "Honestly, it means a lot to me that you came and watched my match. It's been one of my dreams to see you in real life. So when I saw both of you I got really, really nervous."
The No. 10-seeded Navarro beat defending champion Barbora Krejcikova in the previous round, ensuring there will be yet another first-time champion. It will be the ninth different women's champion in the past nine editions of Wimbledon. Serena Williams was the last repeat champ in 2016.
With Navarro's defeat, No. 13 seed Amanda Anisimova is the only American woman remaining in the singles draw; she plays Russian Anastasia Pavlyuchenkova on Tuesday for a spot in the semifinals.
Andreeva, meanwhile, will next face Belinda Bencic, who will also be playing in her first Wimbledon quarterfinal.
ESPN Research and The Associated Press contributed to this report.