Tennis greats Martina Navratilova and Lindsay Davenport took Naomi Osaka to task on Friday, saying she had failed to keep to "basic etiquette" after her Australian Open flashpoint.
Order of Play | Watch Live on DStv
The Japanese star's second-round win against Sorana Cirstea was marred by a testy exchange and icy handshake at the end.
Veteran Cirstea, in her 18th and last visit to Melbourne Park before retiring, took issue with Osaka shouting "come on" between the Romanian's first and second serves.
During her on-court interview, two-time Australian Open winner Osaka was dismissive of Cirstea, but later apologised for being "disrespectful".
"I can get what (Osaka) said after the match because it's kind of in the heat of the moment – she was surprised by Cirstea's reaction at the handshake," 59-time major champion Navratilova said on the Tennis Channel.
"But you cannot be talking out loud between first and second serves of your opponent.
"Cirstea was ready to hit the second serve and Osaka said 'come on' – that's not right. I don't think she does it on purpose, she doesn't realise it.
"You can say 'come on' all you want but keep it inside, do not verbalise it."
Fellow American Davenport, the 2000 Australian Open champion, said she did not expect Osaka to do it again in her third round against Australian qualifier Maddison Inglis.
"Osaka's 28 years of age, she's played tennis for a long time, it's just something you don't really do," Davenport said on the same programme.
"We all know Osaka doesn't have a mean bone in her body, so I would be surprised if she continued with that behaviour.
"You can pump yourself by hitting your thigh (but) you can't yell out in between serves. Basic tennis etiquette 101."
Cirstea was keen to play down the row in her post-match press conference, insisting there was "no drama".
"It was just a five-second exchange between two players that have been on tour for a long time. It stays between us," she said.