India sealed a 21-run win against Australia via DLS method in the first women's T20I at Sydney Cricket Ground on Sunday. India pacer Arundhati Reddy recorded figures of 4-22 while spinner Shree Charani claimed 2-14 in three overs as Australia were bowled out for 133 in 18 overs. India were 50-1 in 5.1 overs while chasing before rain stopped play.