The four-time grand slam champion was given free passage through to the last eight at the Qatar Open after opponent Lesia Tsurenko, of Ukraine, withdrew because of injury.
Osaka returned to the tour in January following the birth of daughter Shai last summer and had won only one of her first four matches prior to heading to Doha.
But the Japanese star has hit form in the Qatari capital, reversing her Australian Open loss to Caroline Garcia in the first round and then defeating Croatia's world No.67 Petra Martic 3-6 7-6 (11-9) in the second.
It is her best run since she reached the final of the Miami Open in April 2022, where she lost to Iga Swiatek.
Top-seed Swiatek breezed into the last eight, where she will face two-time Australian Open champion Victoria Azarenka, with a comfortable 6-1 6-4 win against Russia's Ekaterina Alexandrova.
Azarenka upset Latvian eighth seed Jelena Ostapenko 6-0 6-3, while third seed Elena Rybakina came through three tough sets against American Emma Navarro 6-1 6-7 (6-8) 6-4.
American Danielle Collins and the Czech Republic's Karolina Pliskova also progressed, beating Katerina Siniakova and Linda Noskova respectively.
Wimbledon champion Marketa Vondrousova's difficult start to the year continued with a 7-5 6-3 loss to Anastasia Pavlyuchenkova, while Australian Open runner-up Zheng Qinwen was beaten 7-5 6-3 by Canada's Leylah Fernandez.
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