Australia 178 for 8 (Healy 66, Ecclestone 3-34) beat England 177 (Sciver 64, Perry 3-43) by two wickets
Australia - led by the bowling of Ellyse Perry and the batting of Alyssa Healy - have claimed early Ashes honours, winning a tight opening contest by two wickets in the first one-dayer at Leicester.
England never recovered from a top-order batting collapse, led by Perry's three wickets, despite the best efforts of England spinner Sophie Ecclestone, who claimed 3-34 as the tourists wobbled in their modest run chase. They reached the target with 45 balls remaining on the back of Healy's half-century but, in the face of some tense moments, the match was close, peppered with some poor shot selection, particularly from England, and nervy fielding on both sides.
The loss ended England's winning streak across all formats at 14 after they crumbled to 19 for 4. Player of the Match Perry had Amy Jones out attempting a pull which ballooned to Healy behind the stumps and accounted for Jones's fellow opener, Tammy Beaumont, who chopped on a short time later.
Megan Schutt bowled Sarah Taylor with an in-swinger and then Perry had Heather Knight out lbw for a duck, walking across her stumps.
It became 44 for 5 for England when Fran Wilson was out to a dubious lbw decision to spinner Jess Jonassen. Replays showed Wilson clearly gloved the ball first but, with no DRS for this series, Wilson could do nothing but march off the field making no secret of her consternation.
Natalie Sciver launched a salvage mission with a spirited 64 off 95 balls but when she and Katherine Brunt were out lbw, to Jonassen and Delissa Kimmince respectively, and Anya Shrubsole was caught brilliantly by a leaping Rachael Haynes at mid-off, it fell to Ecclestone to carry on the attempted fightback.
Ecclestone showed fine touch, reaching 27 of as many deliveries, including five fours, but her cameo ended when she attempted to loft Ashleigh Gardner for a second four in a row but found Beth Mooney just inside the long-on boundary.
Laura Marsh was left standing unbeaten on 24 off 52 when Schutt bowled Kate Cross with a beautiful leg-cutter which clattered into off-stump.
Chasing just 178 for victory, Australia more than fancied their chances. Despite the early loss of Nicole Bolton, caught behind attempting to drive Shrubsole, the tourists were in control at 41 for 1 after the first Power Play.
But Brunt, celebrating her 34th birthday and in the rare position of first-change bowler, made the breakthrough with the first ball of her second over when she had Meg Lanning out to a plumb leg-before decision.
Sarah Taylor's stunning glovework shone as usual with a leg-side stumping to dismiss Perry cheaply off the bowling of Sciver.
The England bowlers kept the pressure on Australia by claiming wickets at fairly regular intervals, including that of the dangerous Healy - who reached 66 off 71 balls before holing out to Wilson off Marsh. By the time Marsh bowled Mooney, attempting a paddle-sweep, Australia were 150 for 7 and, while the run rate required was easily attainable, England were in with a sniff if they could just take the remaining wickets.
Shrubsole put down what should have been a regulation caught-and-bowled off Kimmince, demonstrating the less-than-assertive fielding that had bothered both sides at times. Orthodox spinner Ecclestone gave England a glimmer of hope with her penultimate ball, when she tempted Jonassen into a stroke that went straight to Shrubsole at mid-on.
Needing 11 runs off the last 10 overs, the Australians held their nerve, Kimmince struck a lofted four off Brunt which had everyone's hearts in their mouths as it went just wide of star fielder Wilson and five wides off the next ball sealed a low-key end to a thrilling contest.
Both sides admitted nerves were a factor, with England captain Knight putting the hosts' batting collapse down to "maybe absorbing pressure a little bit more".
"Disappointed with the bat, we lost too many early wickets and that ultimately cost us," Knight told Sky Sports. "I'm really proud of the way the girls managed to get us to a total, would have liked a few more, but not to be today. I don't think it was particularly being too aggressive that cost us the wickets. It's maybe a few soft dismissals instead."
Australian captain Lanning said her side would be looking to improve going into Thursday's second ODI.
"Our bowlers did really well to put England on the back foot early but England bowled well as well so it's just nice to get over the line," Lanning said. "Hopefully the quality improves over the series. It was a great contest and everyone fought really hard but we feel like we've got a little bit to work on, as probably England do as well."
The Ashes will be decided over three one-dayers, a four-day Test and three T20Is.
