Napoli coach Luciano Spalletti conceded the race for the Scudetto was no longer in his side's hands after they fell to a 3-2 loss to Fiorentina.
Dries Mertens cancelled out Nico Gonzalez's first-half opener at the Diego Armando Maradona Stadium, before Jonathan Ikone and Arthur Cabral put the visitors two goals to the good.
Victor Osimhen pulled one back in the closing stages for Spalletti's side, but his efforts were ultimately in vain as Napoli succumbed to their sixth league loss this season, five of which came at home.
The defeat leaves them level on points with defending champions Inter, who have played a game fewer, and two behind Serie A leaders Milan ahead of the Rossoneri facing Torino on Sunday evening.
With that deficit in mind, a visibly disappointed Spalletti acknowledged to DAZN that the race for the Serie A title was now out of Napoli's control, and they would need favours from others to win a first Scudetto since 1990.
"Yes [it changes the title race], now everything is getting harder," he said.
"We have no choice but to be professional. Now, we think about winning the next game, even if now it depends on others and not on us."
The Italian also believes the "costly" loss to Fiorentina was undeserved.
"This is a very costly defeat and in some ways undeserved," he added. "Fiorentina played their game and earned the win, but we started strong, then tried to play too long and allowed them to take control of midfield.
"When we conceded the second goal, it all became far more difficult. We have to take some blame for what happened, but it's so disappointing because the fans, the attitude of the whole team throughout the week was the right one."
As for Napoli's disappointing home record, Spalletti claims he does not see a pattern within their home reverses, which he said should be evaluated separately.
"The matches must be evaluated game-by-game," he added.
"I don't see anything similar to the other games, I don't see a sure problem."
Napoli will look to make amends when they host Roma in Serie A on Monday, after Fiorentina became the first side to beat them twice on their own turf in one season since Lazio in 2014-15 (Fiorentina also eliminated Napoli from the Coppa Italia in Naples).