Adrian Mutu opened the scoring in the 14th minute and Gergely Rudolf equalized for Debrecen in the 38th. Fiorentina then took control over a nine-minute span in the second half, with goals from Dario Dainelli, Riccardo Montolivo and Marco Marchionni.
Adamo Coulibaly pulled one back for Debrecen in the 70th and Alberto Gilardino restored Fiorentina’s three-goal lead in the 74th.
Lyon leads Group E with 10 points after drawing 1-1 with Liverpool. Fiorentina is next with nine, Liverpool has four and Debrecen none.
“We’ve got to stay calm and continue playing like this,” Vargas said. “We’ve still got two games to go and it’s going to go down to the end.”
There were also seven goals scored when Fiorentina beat Debrecen 4-3 in Hungary two weeks ago.
With Fiorentina missing goalkeeper Sebastien Frey and playmaker Stevan Jovetic, Mutu set the tone by bending over to head in a bouncing cross from Marchionni for his third goal in this season’s competition – having scored twice in the first game against Debrecen.
A header from Gilardino hit the crossbar in the 34th. But Rudolf equalized four minutes later, scoring with an acrobatic shot from the center of the area.
Dainelli’s header in the 52nd was his first goal in Europe. Montolivo then redirected a cross from Juan Vargas in the 59th for his first Champions League goal, and Marchionni slipped through Debrecen’s porous defense to make it 4-1 two minutes later.
Fiorentina coach Cesare Prandelli was livid after Coulibaly was left all alone to score with a header in the 70th.
The Tuscan club’s reserve goalkeeper, Vlada Avramov, playing his first game in Europe, got a hand on the shot but couldn’t stop it.
Italy center forward Gilardino then rounded out the scoring with a header following a free kick from Vargas.
Debrecen defender Adam Komlosi was hit on the head in the seventh minute and exited bleeding. He was substituted by Zoltan Kiss.
Fiorentina also made a defensive change in the first half, with Alessandro Gamberini leaving with a muscle problem to be replaced by Per Kroldrup.