Naomi Osaka earned a heated Australian Open win over Sorana Cirstea as defending champion Madison Keys, Iga Swiatek and Amanda Anisimova all advanced.
Four-time Grand Slam champion Osaka, who lifted the Australian Open trophy in 2019 and 2021, recovered from a second-set blip to defeat Romanian Cirstea 6-3 4-6 6-2.
Cirstea complained to the umpire over a shout of 'C'mon' from Osaka in the seventh game of the third set, and the Romanian made her displeasure clear after the Japanese star clinched victory.
The pair barely exchanged a handshake over the net, with Cirstea glancing in Osaka's direction briefly and then turning her head away.
As they walked toward the umpire's chair, Osaka asked: "What was that for?"
Cirstea responded directly to the two-time Australian Open winner, apparently upset with Osaka's efforts to pump herself up during the match.
Osaka turned again and waved to the crowd, and in a later on-court TV interview tried to explain what happened.
"Apparently a lot of 'C'mons' that she was angry about but whatever," Osaka said. "I mean, I tried to play well, I tried my best. She's a great player - I think this was her last Australian Open so, OK, sorry she was mad about it."
When asked to clarify why the tension heightened, Osaka said: "She could have asked me to stop."
Cirstea will retire at the end of the season and she bit back at questions about the incident during her post-match press conference.
"I will not talk about that," said the 35-year-old. "This is my last Australian Open. I have been playing for 20 years. It's more going on than a five-second discussion at the end that I had with Naomi.
"There was no drama. It was just a five-second exchange between two players that have been on a tour for a long time. It stays between us."
While Cirstea was keen to move on, Osaka was left with some regrets about the way she had handled the situation.
"I've never been involved in something like this before so I don't know if we're supposed to leave it on the court and be like, 'Hey, how you doing'," she said when asked whether she would speak to Cirstea.
"I'm a little confused. I guess that emotions were very high for her. I also want to apologise. I think the first couple of things that I said on the court were disrespectful. I don't like disrespecting people. That's not what I do.
"So, if she wants to talk about it, then yeah. But, when I'm pumping myself up, in my head I'm not like, 'OK, now I'm going to distract the other person'. It's purely for me.
"No one's ever complained about it before. Also the umpire didn't tell me I was wrong. The umpire said I was fine. I was like, 'OK'. That was kind of what I thought. I thought we moved past it."
Osaka's response to Cirstea complaining to the umpire was to let out extra loud 'C'mons', with the former champion not losing another game.
"I'm not a person that reacts well to being casually disrespected," she said. "I probably overdid it in the next couple of points. But it takes a lot out of me. I'm very tired now."
Osaka's grand fashion statement went viral before her opening win on Rod Laver Arena.
In the second of the show courts at Melbourne Park for her second-round match, Osaka dispensed with the couture wide-brim hat, veil and parasol but still wore the jellyfish-inspired dress.
Instead, she matched a warm-up jacket in the same blue and green aquatic hues as her Nike dress and wore a visor.
Madison Keys overcame struggles with her game to advance to the third round of the Australian Open with a 6-1 7-5 win over Ashlyn Krueger.
The 30-year-old was once again less than convincing in her victory, two days after labouring in a first-round win over Ukrainian debutant Oleksandra Oliynykova.
Keys took 23 minutes to claim the opening set with a confident display that saw the American hit seven winners and convert all three break points against her compatriot in a one-sided start to the contest.
But the current world No 9 allowed doubts to creep into her game in the second set, handing Krueger two breaks in serve with a succession of double faults that saw the 21-year-old open up a three-game lead.
Keys responded, however, by winning five games in a row to close out the match and progress to the next round.
"I started really well, and I think Ashlyn started a little slow, and then I was fully expecting her to raise her level, which she did," Keys said.
"Once I kind of got that momentum, I tried to sink my teeth into the set, and do whatever I could to get back into it."
Six-time Grand Slam champion Iga Swiatek cruised past Marie Bouzkova with a 6-2 6-3 victory as she hunts for her first major title in Melbourne.
"It felt great playing today, I felt more free than in the first round so I wanted to go for it," Swiatek said.
"The conditions were not easy, I don't know if you can tell. It's super windy, so I needed to adjust to that so I'm happy for the performance for sure."
"This is not going to sound like I'm humble, but after winning so much, it's hard to appreciate one match. I'm usually happy after I finish the whole tournament if I win," she added.
"If not, I'm a bit less happy but I for sure have to learn to appreciate every match and not take everything for granted and play to win. It was a good day today and I felt good."
Fourth seed Amanda Anisimova saw off Katerina Siniakova 6-1 6-4 and sixth seed Jessica Pegula thumped doubles partner McCartney Kessler 6-0 6-2.
Former world No 1 Karolina Pliskova, who had two surgeries on her left ankle last year and played only three games, defeated Indonesian Janice Tjen 6-4 6-4 to reach the third round.
Fellow Czech star, Linda Noskova, defeated Australian wildcard Taylah Preston 6-2 4-6 6-2.
Preston made a strong comeback in the second set but ran out of steam against the 13th seed in the decider.
The 25th seed, Paula Badosa, a semi-finalist in Melbourne 12 months ago, made an early exit, losing to the unseeded Oksana Selekhmeteva 6-4 6-4 in her second round contest.
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