FLORENCE, Italy — Napoli, runners-up in three of the last four seasons, hit back from conceding a contentious early penalty to win 4-3 at new-look Fiorentina in a hugely entertaining start to their Serie A campaign on Saturday.

Napoli were also awarded a controversial penalty, for a foul on Dries Mertens, which left Fiorentina coach Vincenzo Montella fuming especially after Franck Ribery, making his debut for the hosts, had a penalty appeal turned down late in the game.

Napoli's win set up an intriguing early clash with champions Juventus, who beat Parma 1-0 away, on Aug. 31.

"There really is anger, because a mistake can happen but for me to reason that these are penalties and others aren’t, no. I can’t do it. I’m sorry," said Montella.

Napoli suffered an early setback when the ball rebounded off a Fiorentina player's knee against the arm of Piotr Zielinksi at point-blank range in the middle of a crowded goalmouth.

Even though the Pole knew nothing about it, a penalty was awarded after a long VAR review and Erick Pulgar, recently signed from Bologna, converted on his debut.

Napoli struggled to get going, yet leveled with their first real attack in the 38th minute when Dries Mertens scored with a dipping shot from outside the area which goalkeeper Bartolomej Dragowski got his hands to but failed to stop.

In the next attack, Mertens fell over Gaetano Castrovilli, who was already on the ground, but the referee pointed to the spot, did not review the incident and Insigne leveled.

Nikola Milenkovic headed Fiorentina back on level terms in the 52nd minute, only for Jose Callejon to put Napoli back in front four minutes later with a low angled shot into the far corner.

Substitute and new signing Kevin-Prince Boateng, making his debut for the 11th club of his career, equalized for Fiorentina in the 65th minute.

But two minutes later Mertens found Callejon at the far post and he knocked the ball back for Insigne to head the winner.

Ribery was brought on for his debut and claimed he should have been awarded a penalty when he went down under a challenge from Elseid Hysaj, but the referee ignored his appeals and VAR did not intervene.

"I don't really understand the rule which provoked the first penalty for us, but the rule is there and, although I don't agree with it, it was a penalty," said Montella.

"But explain to me the Mertens penalty. That was simulation by Mertens and nobody said anything. The referee said he saw a foul but VAR is there, so why didn't he use it."

"It's actually easier to accept errors when VAR isn't being used." — Reuters