World number one Sabalenka powered past Romania's Jaqueline Cristian 6-4, 6-1 to book a last-16 meeting with former champion Osaka.

Japan's Osaka, seeded 16th, pounced for a 6-1, 3-6, 6-1 victory over Camila Osorio to avenge a demoralizing first-round loss to the Colombian here last year.

They were joined in the fourth round by the Philippines' rising star Alexandra Eala, who was leading Gauff 6-2, 2-0 when the American retired with a left arm injury.

Gauff said the pain "felt like a firework going off inside of my arm, and then my whole arm felt like it was on fire.

"And then as the match played, it got progressively worse, even on shots that I wasn't even using my left arm for ... it was a scary feeling."

Gauff trailed 5-2 in the first when she took a medical timeout, a trainer massaging and manipulating her left arm and shoulder.

After Eala broke to take the set on a double fault from Gauff the trainer wrapped her left forearm.

It was to no avail, and after 54 minutes Gauff went to the net and told Eala she was calling it a day.

"I really didn't want to win this way," said Eala, who was cheered on as usual by a big contingent of Filipino fans.

"But this is still a really big moment for me to be able to play on Stadium One of Indian Wells and against such a great competitor," she added, wishing Gauff a speedy recovery.

Earlier action was relatively drama-free.

"So many things I felt like I did great today," Sabalenka said after overpowering Cristian with a performance that included 23 winners. "Serving well, happy with the way I stayed focused no matter what (and) of course happy with the win."

Sabalenka is chasing a first title in the prestigious ATP and WTA Masters 1000 event after twice coming up empty in the final.

Osaka won her first title in Indian Wells in 2018, going on to win the US Open that year in a run that included a victory over Sabalenka.

That's the only meeting to date between the two -- who are now both four-time Grand Slam champions.

"I'll have a chance to get a revenge, hopefully," Sabalenka said.

- Attitude adjustment -

Osaka, playing her first tournament since withdrawing before her Australian Open third-round match with an abdominal injury, roared through the opening set against Osorio but lost her way in the second.

The Colombian broke Osaka for a 4-2 lead and fended off a break point in the ninth game to take the set.

That proved the end of her resurgence. Osaka broke on the way to a 3-0 lead in the third as she brought it home without facing another break point.

"I can only say that I tried to be more positive," said Osaka, who said she let frustration with her mistakes "consume" her.

"I feel like the second set I was complaining a lot and then I just kind of thought my daughter could be watching me mope around the court.

"So I needed to pick up my attitude and that's kind of what I did in the third."

Sixth-seeded Amanda Anisimova and seventh-seeded Jasmine Polini moved safely into the last 16.

American Anisimova needed just 52 minutes to rout 2021 US Open champion Emma Raducanu of Britain 6-1, 6-1 while Italy's Paolini beat Aussie veteran Ajla Tomljanovic 7-5, 5-7, 6-1.