Opting to field after winning the toss, England restricted the Australians to 149 for eight at the Brabourne Stadium.
Rachael Haynes top-scored for Australia with a 65 off 45 balls, knock that included eight boundaries and a six.
For England, medium pacer Jenny Gunn and Sciver finished with three and two wickets, respectively.
In reply, the English team chased down the target with as many as three overs to spare.
The chase turned out to be a walk in the park as Sciver (68 not out off 43 balls) and Beaumont (58 not out off 44 balls) forged an unbeaten 116-run partnership for the third wicket in just 73 balls.
Beaumont and Sciver, who play in the Women's Big Bash League, took a listless Australian bowling to task as they overhauled the target with plenty to spare.
In the process, they steered the team out of trouble from 34 for two.
The carnage began in the sixth over with the right-handed Beaumont hammering four consecutive boundaries off Megan Schutt, as England raced to 51.
Sciver too joined the party as she hit two sixes in the eight over and followed it up with three fours in the 10th.
Australia tried as many as seven bowlers, but nothing stopped the brutal assault of Beaumont and Sciver and the sloppy fielding by the Aussies only aided them.
While Beaumont struck eight boundaries, Sciver hit 10 fours and two sixes in their respective knocks.
Earlier, a brisk 65 off 45 balls from skipper Haynes steered the Australia women to a decent total. England bowlers put a disciplined performance as they took Australian wickets at regular intervals and never allowed their batswomen to settle down.
Haynes posted her highest individual T20 score, as she hammered the English bowlers around the park, but she failed to find support at the other end.
Australian openers - Alyssa Healy (31 off 23 balls) and Beth Mooney (4) - had put on 26 runs before debutant Katie George affected a smart run-out off her own bowling to dismiss Mooney in the fourth over.
It was Healy, who gave the much-needed momentum, as she hit two fours and two sixes in the first six overs.
After Mooney failed, Ashleigh Gardner (28 off 16 balls) played her role to perfection as Australia managed 49 runs in the powerplay period.
The eighth over bowled by Sciver was a dramatic one that saw two wickets and two sixes.
On the first ball, Healy was brilliantly caught at deep square-leg by Danielle Wyatt. Then Gardner struck two massive sixes, but on the last ball, Sciver dismissed the batter to leave Australia tottering at 66 for three.
Australia were poised for a big score as they had amassed 79 runs in the first 10 overs, but then apart from Haynes, no other batter contributed.
Elyse Villani (4), Ellyse Perry (2), Sopihe Molineux (6), Delissa Kimmince (1) failed to support their skipper.
This was Australia's first loss in the tournament after they had convincingly defeated hosts India by six wickets yesterday.
Brief Scores: Australia Women (149/8 Rachael Haynes 65, Alyssa Healy 31; Jenny Gunn 3-26 ) in 20 overs lost to England Women (150/2) Natalie Sciver 68 not out, Tamsin Beaumont 58 not out; D Kimmince 1-12) in 17 overs by eight wickets.
Alyssa HealyAustralian Women's Cricket teamDanielle WyattElyse VillaniEngland Women's Cricket teamNatalie SciverTamsin BeaumontWomen's T20 series
First Published: March 23, 2018, 1:21 PM IST