Tanja Grunwald looked to take control of possession in the midfield, and create attacking opportunities, but she was often left without options to push the ball forward, as Athletic were hungry to score their first goal of the season.
And score they nearly did, with one attacking play allowing right wing Eilish Graves to free striker Rose Lockett, who had made a good run to get in behind the United defensive line and give herself a sight on goal.
The resulting shot was inches away from finding the inside of the right-hand post, having beaten the keeper, with sighs of disbelief ringing out from the Athletic supporters around the park.
United took control of the match again, and managed to slot away two extra goals, including a clinically finished header on the back post from a corner, to take the score to 4-0 by halftime.
Sheena Kahl had her work cut out during the second half, but was immense in the defensive line, spoiling attack after attack with solid tackles, and stamping her authority as she controlled the defensive line.
It was clear the lack of fitness was already taking its toll at the interval, with the visitors jogging off the pitch as a unit, while the Athletic ladies were dispersed around the pitch seeking refreshments and making the most of the break to recuperate.
Athletic started the second half strongly, again building some useful attacks, looking to release their wide players to get in behind the United lines.
But they were often shut down, as the more youthful United team were easily able to catch them and cut off any further attacking options.
It was the lack of fitness which was to be the decider in the second half.
United came back on the attack, forcing Athletic to camp in their own half, and left the home side struggling to keep up with the pace of the match.
As the game wore on, Athletic returned to simply trying to clear their lines and go into damage control.
It was also starting to get messy and overly physical at times, as Athletic's frustration started to get the better of them, forcing referee Cerese Kauika to step in and settle the teams down.
At the final whistle, United walked off the pitch dominant victors, but Athletic will take away some positives from the match, with glimpses of good football showing itself during their 90-minutes.
Athletic will now spend the week preparing themselves for a trip to Wellington, and playing on an unfamiliar turf surface, as they come up against Upper Hutt at Maidstone Park.