Almost two years since Maria Sharapova returned from her doping ban, she has yet to regain her former authority on the court, and neither has she shown a hint of remorse.

Both of these points were driven home on Sunday. First Sharapova suffered a 4-6, 6-1, 6-4 defeat at the hands of Australia's local heroine Ashleigh Barty. Then she declined to answer a perfectly relevant question about the challenge of finding an alternative medication to meldonium, which was outlawed by WADA at the start of 2016.

When Sharapova first revealed the details of her positive test, she said that she had used the drug because of a magnesium deficiency and a family history of diabetes. Coincidentally or not, her effectiveness in deciding sets has fallen since she stopped taking it, from a 76 per cent success rate beforehand to 52 per cent thereafter.

Asked whether it is difficult to deal with the physical demands of a grand slam without her former medication, Sharapova put her hand to her forehead, then pursed her lips and replied "Is there another question?"

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Sharapova seems to like acting as if she were the victim. But there are plenty of other players in the locker-room who have expressed dissatisfaction about her acknowledged use of meldonium for ten years. Her notoriety may also help to explain why the Melbourne fans booed her on Sunday, as she returned from what they saw as a tactical bathroom break at the end of the second set.

This was another question that cropped up in the interview room, to her obvious disgust. "Did you think they [the fans] were a bit unfair to you? Did it affect you at all?"

"What do you want me to say to that question?" Sharapova replied. "I think that's a silly question to ask."

Whatever the surrounding issues, the truth is that Sharapova was outplayed. And her opponent thus became the first Australian woman to reach the quarter-finals here since Jelena Dokic a decade ago. In Melbourne last night, the Barty party was well underway.

It is only three years since Barty came back to tennis after an Australian summer in which she represented the Brisbane Heat in the Big Bash League. Striking 39 on her first appearance in Twenty20 cricket, she clearly handles off-spin as confidently as she does topspin.

Should Barty keep her Melbourne Park run going, she could find herself contesting the women's final here at the same moment as her former team-mates are taking the field in the BBL final. Whatever happens, she is already front- and back-page news across Australia – a refreshingly wholesome standard-bearer to counteract the feuds and excuses of Bernard Tomic and Nick Kyrgios.

The quality of Sunday's match might not have been overwhelmingly high, in terms of pure ball-striking, but the drama was irresistible and the home fans were ecstatic when Barty managed to seal her victory with an ace down the 'T'.

Barty is the No. 15 seed here, which on paper makes her twice as good as Sharapova's No. 30. She has a versatile game too, with the volleys of a doubles champion (she won September's US Open with CoCo Vandeweghe) and the best slice backhand in the business.

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What she doesn't have is much pedigree on the singles court at the majors. This will be her first visit to the quarter-finals of a slam, on her 18th attempt. The main reason for doubt was not that Sharapova might outplay her, but that Barty had shown signs of being gunshy against the biggest names in the past.

During last year's French Open, she had backed off while holding a set-and-a- break lead against a still rusty Serena Williams. And were times here when history threatened to repeat.

Barty coughed up 22 unforced errors to lose the first set, and then let Sharapova fight back from 4-0 down in the decider to a nervy 4-3. To her credit, though, she steeled herself and served out the win on her fourth match point.

"The atmosphere was really unbelievable," said Barty, who shares a partly indigenous ancestry with the seven-time slam champion Evonne Goolagong Cawley. "That first match point, my ears were ringing."

Sportingly, Barty also declined to complain about Sharapova's lengthy bathroom break. "There is nothing I can do. I just have to wait, and I know she was playing by the rule book."