England captain Heather Knight hit an unbeaten 75 to lead her team to a two-wicket victory over Australia on Wednesday in the first ODI and level the Women's Ashes series at six points all.

Beth Mooney top-scored for Australia with 81 as the tourists punished some sloppy England fielding to post 263-8 off their 50 overs after winning the toss and choosing to bat in Bristol.

England dropped five chances and missed a chance to stump Mooney, whose innings was the bedrock of Australia's total as wickets tumbled regularly.

Opener Phoebe Litchfield made 34 and Ellyse Perry added 41 before Jess Jonassen chipped in with 30 down the order for the Ashes holders.

Tammy Beaumont (47) and Alice Capsey helped England get off to a flying start in response as they reached 103-1, but the hosts then began to wobble in a game they had to win.

Nat Sciver-Brunt fell for 31 to leave England 163-4, but Knight stood firm amid a lower order collapse that saw her side still needing 29 to win with just two wickets in hand.

Seamer Kate Cross scored 19 off 20 balls in an unbroken stand with Knight, who thumped the winning runs through the covers to complete England's highest ever ODI chase.

"Every game has been so close. It's been an awesome series. I wanted to be there at the end. It was pure joy," said Knight.

"It was hard work out there. I thought it was starting to slip away. Kate Cross, what a hero. She was nervous when she came in but we broke it down. To beat a very good side is outstanding."

Australia's defeat snapped their 15-match winning run in ODIs as England reeled off a third straight victory over the world champions following wins in the final two T20 internationals.

England must still win the two remaining ODIs to reclaim the Ashes for the first time since 2014 after Australia won the one-off Test and first T20.