Defending champion Naomi Osaka of Japan and Greek third seed Stefanos Tsitsipas were both ousted from the US Open by 18-year-olds in epic stunners on Friday at Arthur Ashe Stadium.
Four-time Grand Slam champion Osaka was shocked by Canadian left-hander Leylah Fernandez 5-7, 7-6 (7/2), 6-4 after Spain's Carlos Alcaraz upset French Open runner-up Tsitsipas 6-3, 4-6, 7-6 (7/2), 0-6, 7-6 (7/5).
"Honestly the Alcaraz match gave me motivation and gave me the energy to do the same," Fernandez said. "I saw his match and I saw the way he won and I'm like 'I'm going to do that next now.'"
After the upset, defending champion Osaka announced she was taking a break from playing tennis.
"I honestly don't know when I'm going to play my next tennis match," Osaka said, wiping away tears. "I think I'm going to take a break from playing for a while."
Osaka, who had won her prior 16 Grand Slam matches, was foiled in a bid for her third US Open crown in four years and the first back-to-back title since Serena Williams in 2014.
Alcaraz is the youngest man in the US Open fourth round since 17-year-old American Michael Chang in 1989, and at any Slam since Ukraine's Andrei Medvedev in the 1992 French Open.
"Incredible. Incredible feeling for me," Alcaraz said. "This victory means a lot to me. It's the best match of my career, the best win.
"To beat Stefanos Tsitsipas is a dream come true and to win here is even more special for me."
Osaka had a major meltdown on court during the final moments of the second set after she was unable to hold serve for the victory.
"From the very beginning, right before the match, I knew I was able to win," Fernandez said. "Thanks to New York fans. They helped me get the win."
Osaka, who hadn't played since Monday thanks to a second-round walkover, took the first set in 37 minutes on her sixth ace.
But she was broken in the 12th game of the second set, an errant forehand sending her to a tie-breaker.
That began a sequence of repeated racquet smashings as she was humbled in the tie-break to force a third set.
"I wanted to stay on court a little longer," said Fernandez, who turns 19 on Monday. "One hour was just not enough for me."
Fernandez then hit a forehand winner to break Osaka to start the third set.
Osaka saved two break points to hold in the third game and from there both held to the finish, which came after two hours and four minutes, sending Fernandez against German 16th seed Angelique Kerber in her first Grand Slam fourth round appearance.
"It'll be a battle," Fernandez said. "We're just going to have fun. I'll put on a show like I did tonight."
Fernandez, the daughter of an Ecuadoran father and Filipino-Canadian mother, won her first WTA title in March at Monterrey. She had never beaten so high-ranked a rival as third-rated Osaka and the same was true for Alcaraz when he sent home the men's world number three.
- 'It's kind of bitter' -
Alcaraz became the youngest man to beat a top-three player at the US Open since the rankings began in 1973.
World number 55 Alcaraz next faces 141st-ranked German qualifier Peter Gojowczyk, who ousted Swiss Henri Laaksonen 3-6, 6-3, 6-1, 6-4.
Alcaraz won his first ATP title at Umag in July, becoming the tour's youngest champion since 18-year-old Kei Nishikori in 2008 at Delray Beach.
The teen nicknamed "Next Nadal" was the crowd darling at Arthur Ashe Stadium, with roars erupting as he blasted 33 winners past Tsitsipas.
"Without this crowd, I haven't the possibility to win the match," Alcaraz said. "I was down at the beginning of the fourth set so thank you to the crowd for pushing me up in the fifth."
Tsitsipas opened the final tie-break with an ace but Alcaraz jumped ahead 5-2 and 6-3 before finishing matters with a forehand winner after four hours and seven minutes of play. He collapsed on the court to celebrate.
"It's one of those matches where you feel like you're in control and it doesn't go your way," Tsitsipas said. "It's kind of bitter."
American Frances Tiafoe sprung an upset, ousting fifth-seeded Russian Andrey Rublev 4-6, 6-3, 7-6 (8/6), 4-6, 6-1 in a late-night encounter.
Russian second seed Daniil Medvedev, the 2019 US Open and 2021 Australian Open runner-up, beat Spain's 74th-ranked Pablo Andujar 6-0, 6-4, 6-3. He will next face British 24th seed Daniel Evans.
Women's second seed Aryna Sabalenka of Belarus also advanced with ease, beating American Danielle Collins 6-3, 6-3.