United rose to the challenge of our first-ever European knockout clash, and were ahead after three minutes when Elisabeth Terland fired home.
Melvine Malard set that opener up and got herself on the scoresheet before the break, curling in to put the Reds 2-0 up as half-time approached.
A sensational Phallon Tullis-Joyce save to keep out a free-kick from former United midfielder Vilde Boe Risa was part of a resilient defensive effort that maintained our clean sheet in the second half, before Julia Zigiotti completed the scoring with just under 10 minutes remaining.
Marc Skinner's side will now take the healthy three-goal advantage back to Manchester, and into next Thursday's second leg at the Progress With Unity Stadium.