Australia women 8 for 231 (Blackwell 67*, Villani 38, Hartley 2-40) beat England women 9 for 228 (Winfield 48, Sciver 36, Gardner 3-47) by two wickets
The pressure of the occasion, in front of a sold-out crowd of nearly 4000 at Allan Border Field, was evident throughout a day where several chances went down but neither side's batting could truly break free of a pair of disciplined bowling line-ups.
England squandered a terrific top-order platform in sliding from 1 for 103 in the 23rd over to 228 all out, as Megan Schutt and Gardner made key contributions with the ball. Likewise, Australia's pursuit of 229 for victory seemed to be drifting off course in mid-afternoon, until Garder joined Blackwell for a vital stand worth 39 from a mere 29 balls.
Gardner's innings only lasted 18 balls but featured a pair of well-struck sixes, enough to mean the hosts needed only two runs from the final over. A forthright boundary from Jess Jonassen then settled the issue, despite some typically tight bowling from Anya Shrubsole, Katherine Brunt and Alex Hartley.
The ground staff at Allan Border Field worked through the night until 4.30am to get the ground ready after torrential rain for several days up to Saturday, allowing the match to start on time with Australia's captain Rachael Haynes sending England in to bat. The hope for some early movement with the new ball was overturned by a strong start from Lauren Winfield, Tammy Beaumont and Sarah Taylor, seemingly setting the visitors up for a tall total.
However, the spin duo of Gardner and Amanda Wellington were able to place a clamp on the scoring rate and push England into error - none more pivotal than the misunderstanding between the wickets that had Winfield run out after a sharp bit of fielding from Jonassen. Another key moment arrived when Natalie Sciver, who had been looking fluent, lofted Gardner towards the long-on boundary, where Elyse Villani managed to hang onto the chance while also being able to avoid stepping on the boundary rope by a matter of centimetres.
England could only add another 38 runs from the remaining 45 balls of the innings, leaving Australia with a target well within range even without the batting talents of the injured Meg Lanning, who will not take part in the series. Led adroitly by Heather Knight, the tourists did not make it easy, claiming the wickets of Nicole Bolton and Alyssa Healy within five overs.
Ellyse Perry seemed to be setting herself for a long stay, but was lured out of her crease by a lovely, looping and spinning delivery from Hartley, which stranded the allrounder and left Taylor to complete the stumping. When Tahlia McGrathwas taken by Winfield off Brunt with 44 balls remaining, Australia needed 48 runs with only the bowlers to accompany Blackwell, who had been fortunate to survive a dropped return catch by Hartley on 35.
Gardner, though, proved herself a matchwinner, guided by the deeply experienced Blackwell - who has now played more ODIs than any other Australian woman, surpassing the ICC hall-of-famer Karen Rolton - to use her power game while the vice-captain rotated the strike. A particularly damaging two-ball sequence had Gardner clearing the backward square leg boundary by inches, before Brunt pushed the ball down the leg side and gave up five wides the next ball.
While Gardner sliced a catch off Jenny Gunn with only nine runs required, and Wellington was run out from the final ball of the penultimate over, it was the partnership between the youthful offspinner and the wily vice-captain Blackwell that had turned the tide Australia's way.