Andreescu, who two years ago as a teenager beat Serena Williams to win the US Open, hadn't played a competitive match since the 2019 WTA Finals due to ongoing knee issues.

She was in stunning form before the injury, winning 38 out of 40 completed matches from February to September.

The setbacks continued early this year when her coach Sylvain Bruneau tested positive for COVID-19 upon arrival in Melbourne, with the pair among the passengers forced into 14-days hard lockdown.

The 20-year-old Canadian withdrew from last week's Open warm-up tournament, opting for more practice time, so was unsure how her first competition match in 15 months would go.

The world No.9 looked headed for a comfortable win over Mihaela Buzarnescu, showing streaks of the classy all-court game that helped deliver her maiden major title.

But the Romanian veteran made her work for a 6-2 4-6 6-3 victory, and the game was on a knife's edge at 3-3 in the decider when Andreescu trailed 0-40.

But the former world No.4 showed her self belief to continue to go for her shots to secure the win.

"I feel pretty damn good - today's match wasn't easy at all and I'm super, super happy with how I fought it out," Andreescu said.

She said she took a moment after the victory to soak up the emotion of returning after a year of anguish.

"It means a lot - I took 15 months off and have been through quite a bit during those 15 months and it wasn't easy.

"That moment over there was me realising how it was all worth it.

"I never gave up and I have amazing people around me."

Andreescu said she would have to improve to have any chance of matching her US Open feats in Melbourne, where she's never made it past the second round.

"I was missing a lot of balls but I don't want to be too hard on myself in my first match back," she said.

"But hopefully next match I can raise my level."

Australian Associated Press