Jenny Gunn held her nerve in the final over as England pipped Australia by three runs in a Women's World Cup thriller at Bristol.
Gunn (2-54) conceded just 12 of the 16 runs Australia required from the last six balls and had Ashleigh Gardner (11) caught by Katherine Brunt as the reigning world champions finished on 256-8 in pursuit of England's 259-8.
England are now top of the standings having reeled off four victories in a row since a surprise 35-run reverse against India in their opener, above Australia on run rate after inflicting a first defeat of the tournament on Meg Lanning's side.
Ellyse Perry scored 70 for Australia but she was caught in the deep off Brunt (2-42) in the 47th over with 42 runs required and despite Gardner, Alyssa Healy (14) and Jess Jonassen (14no) biffing boundaries, England held on to secure a first World Cup triumph over their rivals since 1993.
Gunn and Brunt had also made the difference with the bat, powering the hosts over 250 with a potent late stand of 85 in 12.1 overs, after Tammy Beaumont, who smashed 148 against South Africa last time out, compiled a patient 49 from 88 deliveries.
Australia kept England's other centurions in the competition, Sarah Taylor (35), Natalie Sciver (29) and Heather Knight (2), fairly quiet, and when Beaumont chipped a full toss back to off-spinner Gardner and then Danni Wyatt (27) was bowled by Jess Jonassen, England slipped to 174-6 in the 38th over.
Brunt and Gunn, though, hammered a combined eight boundaries, during which time Gunn had a dismissal overturned - wicketkeeper Healy shown to have grassed the ball while trying to grab it with her left hand - and was dropped by Kristen Beams.
Beams (2-44) had earlier struck twice in her first two overs to oust Taylor and Knight; Taylor - fresh from a career-best 147 against South Africa - bowled off an inside edge having become the leading scorer in the tournament, and captain Knight finding mid-off.
Sciver - who, along with Knight, pummelled Pakistan for a hundred earlier in the competition - fell in similar fashion to her skipper down the ground, off Elyse Villani (3-42), though had the mild consolation of passing 1,000 ODI runs, making her the 16th Englishwoman to achieve the feat.
Beaumont and Wyatt added 54 for the fifth wicket, before Brunt and Gunn's entertaining salvo came to an end in the final over when Gunn was stumped off Vilani, Anya Shrubsole (0) picking out Megan Schutt in the deep last ball.
Shrubsole felt she had Nicole Bolton (26) caught down the leg side in the fourth over of Australia's reply, but Bolton survived the review with no clear nick picked up by Ultra Edge.
Bolton and Beth Mooney (31) went on to post 56 for the first wicket, before Mooney, dropped on 27 by Hazell off her own bowling, lofted Alex Hartley (2-31) to mid-off, Winfield taking a fine tumbling catch.
Gunn - into the side for the injured Fran Wilson (ankle) - then found Bolton's edge, Taylor taking an excellent catch up close to the stumps.
Left-arm spinner Hartley ended Lanning (40) and Perry's 57-run stand stand by bowling the former but Villani gave Perry decent support, albeit that she was dropped by Shrubsole at mid-on and had an lbw dismissal against the Somerset seamer overturned having got a faint snick on the ball.
Villani pinged Shrubsole to Gunn at long-on in the 42nd over, triggering a manic period of play in which Australia scored rapidly, Perry was dropped and then caught by Sciver, Brunt bowled Alex Blackwell (21), and Hazell pinned Healy lbw.
Jonassen could have won the match by smearing Gunn's last delivery for six, but could only muster two to deep midwicket, sparking jubilant celebrations.
Elsewhere, West Indies claimed their first victory of the competition with a 47-run triumph over winless Sri Lanka in Derby - Anisa Mohammed taking three wickets and securing a run out Sri Lanka were dismissed for 182.