The Demons were in control from the opening bounce and never relented, piling on goals at regular intervals to earn a 23.16 (154) to 5.5 (35) victory at Tatura Park and move to an 8-8 record to remain firmly in the hunt for a top-six finish.
The free-scoring Casey starred with a devastating eight-goal haul, while Brodie Newman provided the perfect foil with three majors.
Jensen Dowling, Angus Hicks, Timothy Looby and Jordan Loverso each kicked two goals as the visitors spread the scoreboard with ease.
United set the tone early, racing to a 21-point lead by quarter-time after restricting the Bulldogs to just a solitary behind.
Casey opened his account with two first-quarter goals, while Jordan Loverso and Kye Jeffery also found the big sticks as the Demons established a commanding 3.4 (22) to 0.1 (1) advantage.
The visitors lifted another gear in the second term, adding 5.4 while keeping Tatura to just 1.2.
Casey took control with another three goals before half-time, Jensen Dowling and Liam Serra chimed in, and United headed to the main break comfortably in front, 8.8 (56) to 1.2 (8).
Any hopes of a Bulldogs fightback disappeared after the interval as United dominated territory and possession.
Casey continued his remarkable afternoon with two more goals in the third quarter, while Timothy Looby booted two of his own and Angus Hicks, Xavier Maher and Jordan Loverso also added majors.
By the final change the margin had blown out to 84 points, with United leading 14.11 (95) to 2.1 (13).
The final quarter became a procession, as United slammed on another 9.3, with Casey finishing his day with an eighth goal.
Newman came to life late with three final-quarter majors, while Nathan Ferrier, Jensen Dowling, Angus Hicks and Connor Fleming also hit the scoreboard as the Demons finished with their highest score of the season.
Casey was the clear standout in front of goal, while United's even contribution across the ground was reflected in the goal-kicking spread, with 11 players registering majors in an impressive all-round performance.
The comprehensive victory keeps United entrenched in the congested race for the finals, with the Demons sitting fifth on the ladder heading into the closing rounds, level on wins with Rochester and Mooroopna but ahead on percentage.
“We’re really happy with the with the group, I felt it was a pretty mature win the end,” United co-coach Trent Freer said.
“In saying that too, also Tatura has improved a hell of a lot since we played them at the start of the season, so we knew that we're gonna be in for a fight especially early in the game.
“So I felt that the boys really stuck to task and after a little bit of a bumbling start, I felt that really started to hit our straps, with big Caso (Casey) up forward getting the finishing touches on things.”
