Sabalenka produced an impressive display against a battling Osaka to win 7-5, 6-3 and reach the last eight for a 14th consecutive major tournament.
The Belarusian is now the only Grand Slam champion left in either the men's or women's singles draws at Roland Garros.
"I'm mostly happy with the way I served and I was able to keep all the pressure on her," said Sabalenka.
"I didn't expect I would serve that great... I feel like I'm getting better and better with every match I play and overall I'm super happy with how I played today."
She made it three straight wins against Osaka this year, having lost their only previous meeting at the 2018 US Open.
Sabalenka will next take on Russian Diana Shnaider as she continues her bid for a maiden French Open crown and to banish the memories of her painful final defeat last year by Coco Gauff.
Japanese star Osaka, again sporting the sequined gold dress she likened to the Eiffel Tower at night, has to make do with her best-ever run in Paris, ending in the last 16.
It was the first women's match to feature in the French Open night session since 2023, after a run of 32 consecutive men's ties which drew repeated criticism of tournament organisers.