Osaka had to dig deep for a hard-fought 7-6 (7-5) 6-7 (3-7) 6-4 victory over 17th seed Jovic, in a match lasting two minutes short of the three-hour mark, while Sabalenka had a more comfortable afternoon in disposing of Australian Daria Kasatkina 6-0 7-5.
Osaka's decision to play in a gold sequined top and skirt in Paris drew criticism from her first-round opponent Laura Siegemund, who said she was "not here for a fashion show" after exiting the tournament in a straight-sets defeat to the four-time Grand Slam champion.
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But it has far from deterred Osaka, who has added different variations to her outfit when walking on court for each round, with a metallic gold bomber jacket this time offset by a tannish-gold train.
"It's a surprise every time," Osaka said in her on-court interview after clinching a place in the French Open fourth round for the first time in her career.
The former world No 1 wasted two set points at 6-5 in the first set, and needed three more before taking the opener in a tie-break.
It was a similar story in the second set, with both players earning a break apiece, but Jovic this time triumphant in the breaker to force a deciding set.
The third was again on a razor's edge, with Jovic refusing to buckle and matching Osaka's power blow for blow, until Osaka carved out a match point at 5-4 on the American's serve and converted it to book a meeting with Sabalanka in the last 16.
"Today I was a lot calmer than my first few matches," Osaka said. "I think in Slams, the further I get, the calmer I am - because it's such a privilege to be here.
"I've never been to the fourth round of Roland-Garros before. This is my first time; I'm just really grateful."
In a tournament full of upsets so far - particularly in the men's draw - Sabalenka restored some order when storming the first set against Kasatkina without dropping a game.
Kasatkina, ranked 53rd in the world, broke and held against the run of play to start the second set, but Sabalenka would swiftly restore parity with a break for 2-2.
The four-time Grand Slam champion stayed in touch before dialling up the intensity late on to complete her eighth victory in 10 meetings between the pair.
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