In the one of two matches with seeded players facing off, ninth seed Belinda Bencic came from behind to defeat eighth seed Barbora Krejcikova. Paula Badosa rolled past Nadia Podoroska to complete the quarterfinal lineup.
Vondrousova, Giorgi pull off big upsets; other seeds advance
Vondrousova pulled off the upset in relatively easy fashion, defeating Osaka 6-1, 6-4.
Following the match, the Czech said "I think this is one of the biggest [wins of my career] for sure. I think Naomi, she is the greatest now, the greatest in the game, and she's also the face of the Olympics."
Svitolina had a far tougher challenge, overcoming 14th seed Maria Sakkari 5-7, 6-3, 6-4, her second consecutive three-set match. Bencic dealt Krejcikova just her second loss in the last 24 matches by a 1-6, 6-2, 6-3 score.
Pavlyuchenkova's incredible run continues as she again had no difficulty, this time ousting Sara Sorribes Tormo 6-1, 6-3. The Russian Olympic Committee representative hit 25 winners and won 19 of 26 points at net.
Giorgi needed just 75 minutes to take care of Pliskova as the Italian converted all four of her break points and won 85 percent of her own serve points.
Muguruza continues her solid form and looks to be the new favorite after clinically beating Alison Van Uytvanck 6-3, 6-1. The Spaniard has yet to drop a set in Tokyo and defeated the Belgian for the fourth time in five career meetings.
Rybakina saw off Donna Vekic 7-6 (3), 6-4 after falling behind an early break in the second while Badosa needed an hour, 24 minutes to take of Podoroska 6-2, 6-3 to make it two Spaniards in the last eight.
In second-round doubles action, Krejcikova rebounded from her loss in singles to partner with Katerina Siniakova as the top seeds knocked out Badosa and Sorribes Tormo 6-2, 5-7, [10-5]. Fourth seeds Bethanie Mattek-Sands and Jessica Pegula rolled past Alize Cornet and Fiona Ferro 6-1, 6-4.