Wednesday evening had seen their Reserves hit Cambridge City Development 6-0 in the Cambridgeshire Junior Cup Final and on Thursday it was the turn of the rivals' senior sides.
United play two levels above the recently-crowned Eastern League Division 1 champions and raced into a 2-0 lead inside 10 minutes.
Ashley Deacon cut the ball back for Paige Logie to flick the ball in off the crossbar, before Laura Mills picked out Deacon at the far post to net the second.
It was 3-0 on half-time when Mills whipped in a corner and it found its way into the net, via the unfortunate Tee Mhundura in the City goal.
But City pulled one back with a great strike from outside the area by Charlotte Gillies.
In the 63rd minute, Laura Bright's deep free kick was volleyed into the top corner by Deacon.
Then in added time, Sarah Wiltshire's free kick was saved superbly by the City keeper but Deacon was on hand to tap home the rebound for her hat-trick.
Images - Gary Reed Photography