Set 160 to win on the final day at the Sydney Cricket Ground after England added 40 to their overnight score for the loss of their final two wickets, Australia stumbled their way to 121-5 before Alex Carey (16no) and Cameron Green (22no) ticked off the remaining 39 runs required to avoid an embarrassing final defeat.
Josh Tongue (3-42) was incisive with the ball again for England, taking his wicket tally to 18 over the final three Tests, and making his omission for the first two even more glaring.
He should have added Marnus Labuschagne to his haul, only for Jacob Bethell to make his first error in the Test when putting down a sharp chance at gully when Labuschagne, who was eventually run out for 37, was on 20.
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England might also wonder what might have been had Jake Weatherald been dismissed for 16 instead of 34 as the series was plagued by yet more Snicko controversy.
The third Ashes Test in Adelaide was dominated by doubts over the reliability of the Snickometer technology used to detect edges off the bat, and the issue reared its head again when replays appeared to show a faint nick behind by Weatherald off Brydon Carse, only for the third umpire to fail to give the decision.
Retiring after the Test, Usman Khawaja was dismissed for six in his final innings - bowled off an inside edge by Tongue - as part of Australia's middle-order wobble, before Carey and Green saw the hosts over the line.
The result rubber-stamps a convincing series win for Australia, who had already retained the Ashes within 11 days of action as they won the first three Tests in convincing fashion, before England claimed a consolation victory inside two days on a poor pitch in Melbourne.
It remains to be seen whether changes will be made to the England management team after such a convincing series defeat, with the team's preparation - or lack thereof, having played only one intra-squad warmup game - coming under particular scrutiny.
Captain Ben Stokes is likely to stay in his role, while head coach Brendon McCullum is helped by the fact he is due to lead England's white-ball side in the T20 World Cup beginning in February. Managing director Rob Key could also keep his job, seeing as both were his appointments when assuming his role in 2022.
England give Australia final-day scare in Sydney
England came into the fifth and final morning of the series in Sydney with a 119-run lead and Bethell 142 not out following his magnificent maiden first-class hundred on day four.
He ticked his score beyond 150 but could add only 12 to his overnight total before perishing for 154 to the second new ball, nicking off to a sharp-rising Mitchell Starc delivery that was too close to cut.
Starc (3-72) then cleaned up Tongue (6) to end the innings and take his series-leading wicket tally to a staggering 31 claimed at 19.93 a pop.
Travis Head and Weatherald helped Australia off to a strong start in pursuit of England's seemingly modest target, sharing in a 62-run opening partnership across the opening 10-and-a-bit overs before Head became Tongue's first victim for the innings.
Tongue added Weatherald on the stroke of lunch, with there being zero doubt over his top edge down the throat of deep fine leg following his earlier Snicko reprieve.
Will Jacks bowled a befuddled Steve Smith (12) with an off-spinner's dream delivery - bowled through the gate from the rough outside off - shortly after the interval as England began to believe they could pull off the upset.
England swiftly spurned a couple of chances that would have only added to their growing confidence, Khawaja edging one past Stokes at slip off Jacks and Labuschagne being put down by Bethell off Tongue.
Though both would depart in swift succession soon after, their demise came after Labuschagne hit Jacks out of the attack by smashing 16 priceless runs off his next over.
There'd be no fairy-tale finish for Khawaja, though the 39-year-old did receive a warm send-off from the SCG crowd after his dismissal, while Labuschagne looked utterly crestfallen when run out following one of numerous mix-ups Carey had with his partners late on in Australia's chase.
Australia still required a further 39 runs to win at that stage but despite Carey's dodgy calling between the wickets, he and Green ultimately saw the home side to victory and to a deserved 4-1 series triumph.
Stokes: We play too much 3/10 cricket
England captain Ben Stokes, speaking to TNT Sports:
"I think that for a while now teams have understood how to operate against us. When we get into a situation with the bat where things look easy, opposition teams are doing the same thing to us.
"We need to work out what we do in those situations. We play too much 3/10 cricket in terms of the chances of it coming off, and if you play like that the chances are it is not going to fall your way in big moments.
"We did some unbelievable things as a team the first couple of years in terms of result and getting the best out of people who might not have known they were as good as they were. Now we need to do that consistently.
"How we develop is by being honest and straightforward. You don't progress unless you have those conversations.
"I have been young and had things thrown at me I didn't quite like but I can look back and know that was told to me for the right reasons.
"I just want the best for the guys in the dressing room and to give them the best chance of being very successful international players, which I know they can be. We just need a recalibration."
[On his groin injury]: "I have been better, been worse. I won't know [the extent] until I get home."
'Snicko nonsense shows inequality of system'
Former England spinner Graeme Swann, commentating for TNT Sports, on Jake Weatherald's non-dismissal on 16:
"There was clearly a murmur, exactly the way Stokes was out in the first innings. Herein lies the nonsense of Snicko; it shows the inequality of the system.
"The third umpire has to be held to account. I think that is one of the most ludicrous decisions I have seen in a long time.
"You can't have a system that everyone knows is a joke - how they have kept using it is beyond me.
"It was shown up to be farcical in Adelaide and it has just got worse and worse. The players lose faith and play the system rather than cricket.
"When you have to be strategic about your use of dodgy technology, the world has gone mad. England have every right to be mad and perplexed."
Ashes series in Australia 2025-26
Australia win five-match series 4-1
First Test (Perth): Australia won by eight wicketsSecond Test (Brisbane): Australia won by eight wicketsThird Test (Adelaide): Australia won by 82 runsFourth Test (Melbourne): England won by four wicketsFifth Test (Sydney): Australia won by five wickets