Batting first, Nat Sciver-Brunt lifted Mumbai Indians to 161 for five after a poor start with a brutal 43-ball 65, while Nicola Carey blazed away to an unbeaten 20-ball 32, as the team amassed 107 runs in the last 10 overs.
However, UPW overcame the total with Harleen playing the lead role and Phoebe Litchfield (25 off 22 balls) and skipper Meg Lanning (25 off 26) making useful contributions with the bat.
Chloe Tryon made a brisk 27 not out in 11 balls.