Bianca Andreescu's comeback after a 15-month absence ended abruptly in the Australian Open second round on Wednesday with a 3-6, 2-6 defeat to the wily Hsieh Su-wei from Chinese Taipei, but the Canadian leaves Melbourne Park glad as her "fighting spirit" is alive.

Former U.S. Open champion Andreescu savored an emotional first-up win against lucky loser Mihaela Buzarnescu on Monday but hit a brick wall in the form of Hsieh in the early match at Rod Laver Arena.

"I got off the court and I was looking at my coach, and I said I'm just disappointed that today that was my all because I know I gave my all today and to me I think that was the most disappointing part," 20-year-old Andreescu told reporters.

"I didn't put expectations on myself. There's always unconscious expectations for sure, but verbal expectations, not really.

"So I'm just going to take this as a learning curve and bounce back for the next tournament."

Andreescu, who stunned the tennis world by beating Serena Williams for the 2019 title at Flushing Meadows, attacked Hsieh with her usual gusto but Hsieh, double-handed on both side, was brilliant in defense and confounded the Canadian with an array of drop-shots and angled winners.

With no apparent 'Plan B', eighth seed Andreescu doubled down on the power game and the unforced errors piled up as she slumped to a 5-2 deficit in the second set and then bowed out meekly with a double-fault on match point.

Prior to Australia, Andreescu had not played since the 2019 WTA Finals in Shenzhen and was one of 72 players unable to train during their 14-day hard quarantine in Melbourne.

Adding to the challenges, her coach Sylvain Bruneau tested positive for COVID-19 after landing in Australia last month.

Yet there were no excuses from Andreescu, unlike a number of players who blamed inadequate preparations for their exits.

"I know that my preparation was the best preparation that I think I've ever had," said Andreescu. "So I feel confident with that.

"I think now it's just getting back into play, and it's good to know that I still have that fighting spirit in me.

"I'm able to give it my all on the court. I think you see that more in the first match than this match, but also being healthy.

"I feel really good. After my first round, I thought I would feel more exhausted, but I felt amazing."