Ella Toone opened the scoring after 13 minutes and that lead was doubled before the break in the soggy conditions, through Elisabeth Terland.
Melvine Malard netted United's third and fourth goals of the afternoon in a second half that featured a club debut for Jess Park, who joined from Manchester City on Thursday's WSL deadline day.
FIRST HALF
United started like a team already two competitive games into the season. Fluid with movements, fast on the ball and possessing an intensity without it. It meant we got on top early, with the visitors needing a save from goalkeeper Janina Leitzig to keep out a close-range effort from Toone, who had drifted into the 18-yard area and was found by an incisive Melvine Malard pass through the defence.