It took an 84th minute shot from David Wotherspoon, deflected home by Hearts' Marius Zaliukas, to separate the sides and give the home fans their first derby win in 13 attempts.
The memories of a 5-1 cup final defeat at Hampden in May will never fully clear up but with a derby win to celebrate, Fenlon's name was chanted long after the final whistle by the home supporters.
Fenlon revelled in the result and was delighted with the way that his side is developing after getting the name of being soft touches when he came into the job.
"It wasn't a great spectacle, but we've won and that's all that matters," the former Bohemians boss stated.
"It's a great day for Hibs fans and it's long overdue. It was a scrappy game and Hearts shaded parts.
"There weren't a lot of chances but you take the fortune when it comes. I didn't enjoy the 90 minutes. As a manager you don't enjoy matches, you enjoy the end if you win, you don't if you lose."
The win earns Hibs a place in the fifth round draw of the cup to complement sitting in second place in the SPL.
Fenlon celebrated his first year in charge of the club a week ago and is confident that he has the Edinburgh side moving in the right direction.
"This isn't about revenge, it's about rebuilding this club back to where it should be," he added. "It gives the players and the supporters belief in what we are doing here. It's a victory over Hearts and it means a little more to everyone but it's just another step in the right direction.
"We weren't fantastic, there's a lot of stuff we need to work on still but we would have lost that game last season, no doubt about it.
"We don't look like losing a lot of matches right now.
"Now they can hold their heads up high. They've been in the doldrums for too long and can enjoy themselves."