MIAMI — As Naomi Osaka's 23-match winning streak neared an end Wednesday, she paused before serving to crane her neck and study the sky, as if seeking intervention from above.
Then she carried on, and so did No. 23-seeded Maria Sakkari, who upset Osaka 6-0, 6-4 in the quarterfinals of the Miami Open.
"The more stuff like this happens, the more I'll learn from it," the No. 2-ranked Osaka said.
Osaka's defeat was her first since February 2020, and it ended any chance of reclaiming the No. 1 ranking this week from Ash Barty, who is in the semifinals.
The men's favorite departed nearly 12 hours later when No. 1-seeded Daniil Medvedev lost to No. 7 seed Roberto Bautista Agut of Spain, 6-4, 6-2. Medvedev mangled his racket in anger after he lost serve to fall behind late in the first set, and little went right for him the rest of the way.
"If he broke a racket, it's because he lost his patience," Bautista Agut said. "I think I did some great things to put him under pressure and feel like this."
Medvedev fell to 0-3 against Bautista Agut, one of the six players left in the men's draw. None has won a Masters 1000 event.
Sakkari will next play No. 8-seeded Bianca Andreescu of Canada, who dropped serve eight times but still outlasted unseeded Sara Sorribes Tormo 6-4, 3-6, 6-3.
"I'm super proud of how I handled it tonight, because it wasn't easy," Andreescu said. "My body was giving out, and then my mind gave out at one point, because I was just thinking about how tired I was."
The other women's semifinal Thursday will pit Barty against No. 5 Elina Svitolina.
Osaka won her fourth Grand Slam title at the Australian Open in February, but in five Miami appearances she has never advanced beyond the quarterfinals. She said couldn't get comfortable on the tournament's hard-court surface.
"I felt like I haven't been playing well this whole tournament, like I couldn't find a groove," she said.
Against Sakkari, the only Greek woman ranked in the top 250, Osaka lost 15 consecutive points on her serve to fall behind and blew a 4-1 lead in the second set. She faced a break point on seven of her eight service games.
"Today's service problems kind of came out of nowhere," Osaka said. "My first serve wasn't going in at all today."
Sakkari earned her sixth career win over a top-five opponent. She's still in the tournament only because she saved six match points in the previous round before beating American Jessica Pegula.
In men's play, 19-year-old Italian Jannik Sinner earned his first semifinal berth in an ATP Tour top-level event by beating No. 32-seeded Alexander Bublik 7-6 (5), 6-4.
Bublik smiled as he congratulated the No. 21-seeded Sinner at the net.
"You're not a human, man," Bublik joked. "You're 15 years old and you play like this? Good job."
Sinner will face Bautista Agut on Friday.
Osaka made just 41% of her first serves and paid a price, because Sakkari aggressively attacked the second set. Sakkari also served well and would repeatedly extend rallies until Osaka made an error.
"I don't think it was the best tennis I played in my life," Sakkari said. "I just did what I had to do."
Osaka took a 40-0 lead in the opening game, but didn't win another point on her serve until the second set. When she ended the drought, she received a big ovation from the small crowd, which she followed up with her best stretch of tennis.
But Sakkari rallied. From 40-0 down she won five consecutive points, hitting one last thunderous return to break for a 5-4 lead. She then coolly served out the victory.
"I just really enjoyed myself out there," Sakkari said.