‘Stranger things have happened’: Matildas on upset alert
The Australians will be extra wary of out-of-contention Jamaica, with the 53rd-ranked Reggae Girlz considered dangerous with nothing to lose when they meet in their final Group C.
Early last year, en route to World Cup qualification, they drew 2-2 with world No. 34 Thailand and scraped through to the final on penalties.
Last week the United States walloped Thailand 13-0.
It's why Australia won't be underestimating Jamaica in their final group hit-out in Grenoble on Wednesday (5am).
Even if the Caribbean nation are ranked 53rd and have shipped eight goals from two games at their very first World Cup.
"Different day, different football," Gielnik said.
"Thailand could have had a blinder against America and they just didn't. It's so unpredictable.
"Italy, for instance, weren't the most favoured team and they come out and beat us.
"We didn't play our best football but it just goes to show that unpredictability of all the teams, and most definitely the underrated ones.
"Right now Jamaica have nothing to lose so that makes us vulnerable in a way.
"We have to go out there not taking them as any less of an opponent than anybody else.
"That's important for us, otherwise we don't play our same style of game and we hold back.
"It's the World Cup and stranger things have happened."
Gielnik didn't rule out smashing six past Jamaica, a scenario that could see the third-placed Matildas top Group C if Brazil also see off Italy.
The forward, who played her first World Cup minutes as part of Ante Milicic's starting line-up in Friday's tournament-rescuing comeback win over Brazil, said the squad was still high on the euphoria of that scarcely believable night in Montpellier.
But the 27-year-old clarified the sentiment was not one of overconfidence, just belief and a willingness to improve.
"It's given us that belief and that positivity going forward knowing we feel confidence to win against Jamaica," she said.
"Not just to win but to play our best football and score as many goals as possible without over-thinking the end outcome.
"We are still riding this wave and we honestly just can't wait for game day, it couldn't come quick enough."