Former world No 1 Jankovic was beaten in two contrasting sets by Croatia’s Ajla Tomljanovic, while both Stosur – who had a match point – and Petkovic lost their matches in three.
Jankovic, the No 6 seed, lost 7-6 (8-6) 6-0 to Brisane-based Tomljanovic who is planning to apply for Australian citizenship later this year.
Tomljanovic, the world No 63, edged a titanic opening tie-break in which her opponent held a set point at 5-6.
However, the second set was a lot easier for the 21-year-old who needed just 30 minutes to wrap up the victory.
Jankovic says she is yet to regain full fitness after suffering a back injury towards the end of 2014.
“I was not playing or doing any activities for two months, so it took me a little bit of time to just get active and kind of start doing just normal things, and then kind of getting into the tennis and training properly,” she said.
“It’s not easy. And after not competing, after just practising and just trying to get in form and get in shape I lost my muscles and I looked like jelly.
“When you are injured and you have a bad back injury, you’re thinking maybe you’re never going to be able to play again at a high level.???
Also sent packing was No 5 seed Petkovic who was on court for two hours and 25 minutes before losing to the powerful Kaia Kanepi of Estonia 6-4 5-7 6-4 in the Pat Rafter Arena.
In a match that ebbed and flowed, the final set yielded seven breaks of serve before the world No 51 and former Brisbane champion reached the second round on her first match point.
As for Aussie Stosur, now 30 and ranked 22, she threw away a 5-1 lead in the final set before losing to American Varvara Lepchenko 4-6 6-4 7-5.
Stosur, who resides on Queensland???s Gold Coast, made eight double faults and even held a match point in the eighth game.
World No 2 Maria Sharapova is the top seed.