Goals from Kyogo Furuhashi and David Turnbull gave Ange Postecoglou’s side their first victory in the Europa League group stages.
It also gives them a chance of hauling themselves back into contention for a spot in the knockout rounds if they can repeat the feat when the sides meet against in Budapest in over a fortnight’s time.
Hartson believes the performance on Tuesday evening should give the squad great belief ahead of the return fixture.
He said on BT Sport: “It’s great for confidence going to Budapest in a couple of weeks’ time. They’ll go there knowing they can comfortably win the game.
“All right, it’ll be an away game, but they can comfortably beat this Ferencvaros team, which is what I said beforehand. I really fancied Celtic today.
"It was just a fantastic all-round performance with chance after chance after chance.”