Nineteen-year-old striker Ross Caldwell struck a stoppage-time winner at Tynecastle to hand Fenlon's side a 2-1 win - their first Clydedale Bank Premier League victory in four years.
The Gorgie victory was the second Hibs have enjoyed over their old foes this term after knocking them out of the William Hill Scottish Cup in January.
This season's three other SPL meetings ended in draws, leaving Hearts unable to muster a league victory in the derby for the first time since the 2000/01 season.
All that makes pleasant reading for the Easter Road boss.
Fenlon said: "I certainly enjoyed that and I'm sure the supporters are enjoying it as well, which is great.
"I don't think there's any doubt that we were the better side. I thought the first half in particular we played really well, created some chances but got hit with the sucker punch just before half-time with the goal.
"I don't know if this is a turning point but what we did say is that we wanted to improve and be competitive in all the derbies. Now we've won two, in the cup and in a league game at Tynecastle for the first time in a while. We have alsogone unbeaten against them this season, which hasn't happened in 12 years.
"So it's progress, it's a step on the ladder but we won't get too carried away because we've got a couple more games to go and then a massive cup final. But we'll take great confidence out of this."