Alyssa Healy was back in the runs, Australia were halfway towards their target with a run-a-ball needed and eight wickets in hand to launch a home World Cup campaign a long time in the making. Then it all changed.

The ball after bringing up her fifty with a six, Healy chipped a flighted leg-break back to Poonam Yadav who held her nerve following a big full toss. From there, Australia's innings unraveled as she caused havoc with her googly. Yadav, the leading wicket-taker in T20Is over the last two years, picked up three more in her next 11 deliveries and was only denied a hat-trick when wicketkeeper Taniya Bhatia made her one mistake on an evening where she was otherwise outstanding behind the stumps.

The fact Australia were all but out of the chase come the last over showed how complete the shift to India had been. In the moment it is easy to overstate the importance of something, but this had the feel of a very significant start to the tournament.

With victory in front of a record-breaking crowd for a standalone women's game in Australia of 13,432 - a healthy proportion cheering for the side in blue - India secured a sizeable step towards making the semi-finals. Conversely, if Australia are going to win a World Cup where there is so much expectation they are going to have to take a much harder route than many envisaged just a few weeks ago. They can't afford another slip-up now.

Not that the result itself should be considered a huge shock. Australia were favourites - rightly so - but only a couple of weeks ago India dusted them up in the tri-series (only to lose a final they probably should have won) and have now beaten them in the last three global events: the match at the 2017 World Cup is famous for Harmanpreet Kaur's 171, the match at the 2018 T20 World Cup was less significant as it didn't impact progression for either team - this one feels much closer to the former for impact, although they could yet have to do it again if they want to claim the title.

"She [Poonam Yadav] bowled the first over pretty regulation as a legspinner then slowed it up immensely after that. We probably didn't adapt well enough."
Alyssa Healy

Yadav had not played in the tri-series earlier this month as she nursed an injured finger on her left hand that remained bandage as she smiled her way through the post-match press conference alongside Kaur. "It is painful, but when I play the match I forget it," Yadav said. "Bowling-wise I was confident I could bowl at any time."

During her time sidelined, fitness has been her focus which has included a gluten-free diet that hasn't exactly been to her tastes. "I am surviving on rice which I don't like at all. [They] scold me saying, "no, you are not allowed to eat gluten." They take it off my plate, but I understand that they are doing this for the sake of the team."

Her absence meant Australia had not seen her recently - last facing her in the group match at the 2018 tournament where she claimed 2 for 28 - and when the injury was referenced to Healy she admitted being unaware, saying she thought the tri-series non-selection may have been tactical. As it's turned out, maybe it was a useful coincidence for India.

"We prepared really well," Healy said. "She bowled the first over pretty regulation as a legspinner then slowed it up immensely after that. We probably didn't adapt well enough. We don't get legspinners coming down at 60kph very often and she's incredibly skillful."

While Yadav, who was held back until the 10th over, bowled beautifully after the early full toss, the Australians produced some poor batting and were unable to read her wrong 'un - Rachael Haynes missed by a long way and Ellyse Perry, who slipped down to No. 6 in a curious reshuffle of the batting order, played a loose stroke across the line. Looped up at around 60kph, dipping late on the batters (and even being called no-ball for bouncing twice at one point which denied her a five-wicket haul), it preyed on their eagerness to put bat to ball on a surface that was sluggish and probably aided spinners more than the hosts would have liked.

"We went out thinking it was a flat wicket and played some shots we shouldn't have," Healy said. "Most of the wickets that fell today were batters playing across the line in both innings, so for us we'll have a look at that and say we didn't adapt."

"Poonam did a great job for us, credit goes to our bowlers - they trusted themselves and won the game for us," Kaur said. "She is a very good T20 bowler, she always bowls for the team and it's not easy to play, she is a little slower in the air. When you have to hit her, you have to show patience and very good skill."

Yadav praised the role played by Narendra Hirwani, the former India legspinner, who is on the team's coaching staff. "Mentally he helps us a lot. He talks about understanding the bounce. He talks about we all have variations, but when to use them how to use the bounce and the right areas to pitch."

As it is for Australia, this is just one game for India, but given their victory was also fashioned after a top-order collapse, which was repaired by a career-best 49 from Deepti Sharma in the much-criticised middle-order, it was a win that made a statement. The next couple of weeks will show if they live up to it.

Andrew McGlashan is a deputy editor at ESPNcricinfo