Knowing all three points would cement Victory's spot in the A-League Men's top six, Melbourne came out firing, netting two goals within the opening 25 minutes at AAMI Park on Sunday.
One of those came from Genreau, who scored for the first time since October when Charles Nduka teed up the midfielder and he guided the ball into the bottom right corner.
The strike was his first against his former team after playing for them in the 2020/2021 campaign before departing for French side Toulouse FC.
"I've hit the post two or three times, so it felt really good for it to go in. Obviously, the second goal was really important in a game like this," Genreau told Paramount+.
"Their first goal, they scored from their first shot. That's been the story of our season so far. We need to be better."
Macarthur's young gun Luke Vickery snatched a goal back before Sebastian Esposito and Nduka netted to help Victory claim the win and move seven points clear of their seventh-placed opponents.
Victory also extends Melbourne's unbeaten streak to six games after a disappointing 2-2 draw to Sydney FC last Saturday, when two late goals cruelled their chance of claiming three points.
Macarthur haven't won since January, and the loss won't do them any favours as they remain two points out of the top six with five rounds remaining.
The Bulls were without defender Tomislav Uskok and goalkeeper Alex Robinson after both were handed red cards in their 3-1 loss to Central Coast last round.
"I'm pretty disappointed. I felt like we got beaten by a team that was hungrier and that really wanted to win," coach Mile Sterjovski said.
"We just have to have a good look at ourselves and put in the effort to try and change things around."
Melbourne had a flurry of chances early and found a way through when former Victory defender Damien Da Silva scored an own goal from a Keegan Jelacic cross in the 11th minute.
Victory continued to sniff at goal, and Genreau rewarded their efforts, but 12 minutes later, Vickery curled the ball into the bottom left corner.
The in-form Juan Mata added another assist to his double-digit tally (11) when his corner found the head of Esposito in the 63rd minute.
Just three minutes after that goal, Mata unleashed a driving free kick into the box, and Nduka poked the ball past Bulls keeper Filip Kurto.
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