The scores could not be separated at half-time, while Rochester held a slim two-point buffer at the last break.
But Mooroopna pulled away in the last quarter to emerge a 7.10 (52) to 5.9 (39) winner.
Joss Church kicked two majors for the Cats, while Ben Woods was named best-on-ground for his efforts.
Charlie Palmer kicked two goals for Rochester to be its only multiple goal-scorer and was named best for Rochester.
The win leaves Mooroopna only a game off Rochester on the ladder and will look to close that gap even more when it takes on the Shepparton Swans next round.
Meanwhile, Echuca had a healthy win against Kyabram on Saturday.
The 68-point shellacking keeps the Murray Bombers locked on top of the ladder.
The win adds salt to the wounds for Kyabram, which had been beaten by Echuca by 99 points in round three.
After leading from the onset of the match, Echuca ran out to a 15.10 (100) to 5.2 (32) triumph.
For Echuca, Isaac Watson kicked three goals, while Sam Edgar, Cody Mann, Makai Cronin, Noah Turner and Will Rohde chipped in with two goals each.
Tom Evans was adjudged to be best-on-ground for Echuca.
Bailey Pike booted two goals to be the only multiple goal-scorer for Kyabram, while Kayden Robinson was voted best his efforts.
In a low scoring game at Kings Park, Shepparton got the better of Seymour with a 44-point win.
Seymour was held goalless in the first quarter and had only kicked one goal to three-quarter time in a game dominated by the Bears.
Shepparton's Zaydan Leocata starred with three goals, while Jensen Dowling and Matt Whitlock managed to kick two goals each.
Noah O’Dwyer was named best-on-ground for the Bears, while Jack Whitlock provided great support in the 10.3 (63) to 2.7 (19) win.
For the Lions, Oliver Munro registered their only two majors and Will Le Deux was named their best.
The second week of the split round features Shepparton United taking on Shepparton Swans in a game that could be a preview of what is to come in the finals, while Euroa comes up against Tatura at Tatura Park.
● Ben Andonoudis is currently completing work experience with The News.
