Osimhen hits double in Napoli's winning start to title defence
Nigeria striker Osimhen netted in each half to help ensure the champions came from behind to win on Rudi Garcia's debut as coach following the resignation of new Italy boss Luciano Spalletti.
Matteo Politano scored Napoli's other goal, getting the away side back on level terms midway through the first half after Abdou Harroui had given hosts Frosinone a shock early lead from the penalty spot.
"It was important to start well... the opponent gave us a very hard time," said Osimhen to DAZN.
Osimhen scored 31 times last season, including the goal which sealed the league title and he is in talks for a contract extension despite big-money interest from clubs abroad.
"The president is the boss. We are still negotiating, maybe at the end of the transfer window we will see what will happen," added Osimhen, whose current deal expires in June 2025.
"But for now I'm a Napoli player which is the most important thing and I will give my heart and soul for the team."
Garcia has a tough job on his hands defending Napoli's first championship crown since 1990 and didn't have things all his own way at the Stadio Benito Stirpe.
His team were trailing in the seventh minute when Harroui slotted home a penalty following a clumsy foul from Jens Cajuste, who had a difficult debut.
Cajuste had already flattened a pitchside photographer with a wayward pre-match shot when instead of clearing the ball he booted Jaime Baez and conceded the spot-kick.
Napoli, who were without injured star winger Khvicha Kvaratskhelia, were level when Politano pounced following chaos in the Frosinone box and lashed in a powerful left-footed shot which should have been stopped by home goalkeeper Stefano Turati.
Kvaratskhelia's replacement Giacomo Raspadori thought he had put Napoli in front 10 minutes before the break but the goal was chalked off for the unfortunate Cajuste being offside early in the move.
However there was no stopping Osimhen from crashing in his first of the season in the 42nd minute when Giovanni Di Lorenzo won the ball high up the pitch and fed last season's Serie A top scorer, who thumped home a rocket of a first-time finish.
Baez hit the woodwork with a free-kick in the 57th minute as spirited Frosinone tried to take the game to Napoli.
But Osimhen, who also fizzed a stunning effort just over the bar on the hour mark, sealed the points with 11 minutes remaining after being sent clean through by Di Lorenzo and coolly stroking past Turati.
Later on Saturday, Champions League finalists Inter Milan kick off their campaign with the visit of Monza, while Italy striker Mateo Retegui makes his Serie A debut for promoted Genoa against Fiorentina.