Naomi Osaka has apologised for “disrespectful” comments to her opponent as emotions boiled over at the Australian Open.

The 28-year-old Japanese and Romania veteran Sorana Cirstea exchanged heated words during an icy handshake at the net after Osaka’s 6-3 4-6 6-2 victory on Thursday night.

Cirstea was apparently angry at Osaka saying “come on” to pump herself up and told Osaka after the match: “You’ve been playing for so long and you have no idea what fair play is.”

After the match, Osaka told media: “Apparently, a lot of ‘come ons’ that she was angry about, but whatever. I mean, I tried to play well, I think I hit a lot of unforced errors, but 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.”

But Osaka said she’d never been involved in a similar situation.

“I don’t know if we’re supposed to leave it on the court and be like, Hey, how you doing?” she said.

“I’m a little confused. I guess that emotions were very high for her. I also want to apologise. I think the first couple things that I said on the court was disrespectful. I don’t like disrespecting people. That’s not what I do.

“If she wants to talk about it, then yeah. But, like, 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.”

Osaka will next play Australian hopeful Maddison Inglis in round three.

Also on Thursday, she had appeared to struggle with a shoulder issue but wouldn’t go into specifics on what had required treatment.

“It’s kind of a re-occurring thing. I guess if you look at my medical history, you can maybe do like a little guessing game,” Osaka said.

“I’m just really glad that I kind of pushed through it and also played really good tennis in the third set. I try to just leave the tournament site with that in mind for the next days.”

Osaka came into the Australian summer underdone after a virus and had previously been sidelined by thigh injuries, abdominal strains and a back injury.

Cirstea and Osaka had a frosty handshake after the Romanian’s displeasure at Osaka pumping herself up between Cirstea’s serves.

Osaka, the tournament’s 16th seed, has now won 10 of 11 three-setters at Melbourne Park.

“For me, I go into it knowing that my fitness level is pretty good,” she said.

“I know that I’m fit enough to go into the third set pretty strong. Also I just really love this tournament and I want to stay here as long as possible. That definitely motivates me.”

Osaka was the talk of the Open on Tuesday night when she entered Rod Laver Arena in a couture outfit inspired by a jellyfish.

The look included a dramatic white wide-brimmed hat with a gauzy veil and train, white pants and a white parasol.

It created speculation Osaka could change up her look on Thursday. Instead, she donned a dressed-down version of the previous outfit.

There were two fans in the crowd wearing veils in a nod to Osaka’s fashion statement and she was delighted by the attention it had garnered.

“My simplified look is very extra for some people,” she said.

“I don’t know. I just felt like switching it up. I think it’s kind of fun to keep everyone on the edge. I thought it was really pretty that there were some people with veils over their hats. I was really grateful for that.

“For me it’s kind of cool, like you never know what I’m going to pull out next.”

-with AAP