The 24-year old forward, who joined the Revs from SKC in the offseason, deflected Diego Fagundez's cross from the right into the back of the net in the second minute of injury-time.
Bunbury's goal came prior to Lee Nguyen's penalty and filled the Canada-born USA international with plenty of joy despite the fact it sunk his old teammates.
"Definitely a lot of emotions, but most importantly, I'm just excited that we were able to get a win," Bunbury said.
"Our performance from the first minute to the last minute, I thought was world class. Everybody was fighting, everybody was putting pressure on them and it feels good to beat the former champs.
"It's great - my old club and all that - but to be honest with you, the performance of the whole squad was unbelievable."
Bunbury added: "For me, a goal's a goal. I really couldn't be happier for that. But it's really the work of my teammates that kept my spirits up through these games not scoring yet. So this definitely feels good."
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