Captain Alastair Cook (58) and his old Essex friend Ravi Bopara (52no) kept their cool as the hosts reached a Duckworth-Lewis target of 138 with seven wickets and 11 balls to spare in a rain-shortened match at Old Trafford.
England's change bowlers were to the fore as Australia endured a hapless collapse and mustered only 145 for seven in 32 overs.
But the hosts then lost Ian Bell, previously prolific in this series, to a chip to midwicket off Clint McKay in the first over of their reply.
Progress was also interrupted by a short break as the bad weather, which had delayed the start by three-and-a-half hours at Old Trafford, briefly returned – and left England with an apparently more exacting equation.
Jonathan Trott was then bowled sweeping at slow left-armer Michael Clarke, and Cook and Bopara had work to do from 34 for two in the 10th over.
But England's third-wicket pair did not panic, and gathered gradual momentum to add 92 together – by far the best stand of the match.
Cook adopted the sheet anchor role, on the way to his first half-century of the series from 69 deliveries, and Bopara injected the spark England needed to stay on course in his run-a-ball 50 - his 10th in ODI cricket.
The England captain did not quite see the job through, well-caught at slip by Clarke off Ben Hilfenhaus, but Bopara left nothing to chance. James Tredwell had earlier taken his first home wickets for his country, as the tourists lost four for 12 runs; then Bopara took two for three in seven balls – and despite top-scorer George Bailey's unbeaten 46, Australia's total was decidedly vulnerable.
They were put in under cloudy skies and, after making 43 for none by the 11th over, badly needed to consolidate that encouraging start. Sadly for Clarke's team, they managed nothing of the sort – two run-outs, including the captain's, helping to undermine their efforts.
Australia eventually found themselves on 86 for six and Bailey and the tail tried to salvage a defendable target, managing 58 for one wicket in the last 10 overs.
It was an admirably defiant effort but not enough to rescue any consolation.