The Partenopei could have clinched the title with a record six rounds to spare if they beat Salernitana but Boulaye Dia equalised for the visitors six minutes from time after Mathias Olivera had given Napoli the lead on Sunday.
"The guys are so disappointed they couldn't provide joy to the amazing crowd," Napoli coach Luciano Spalletti said.
The result left runaway leaders Napoli 18 points ahead of second-place Lazio, who lost 3-1 at Inter Milan earlier.
Napoli are attempting to win the Italian league for the first time since Diego Maradona led the club to their only two Serie A titles in 1987 and 1990.
Olivera scored just after the hour mark with a header inside the far post from a corner. Dia then dribbled by Napoli center forward Victor Osimhen and unleashed an angled shot to equalise.
"These are the most difficult points on a psychological level and they take something from you," Spalletti said.
Napoli visit Udinese in their next match on Thursday, but they could win the title before then if Lazio don't beat Sassuolo and Juventus don't defeat Lecce on Wednesday.
Napoli fans had been celebrating inside and outside the Stadio Diego Armando Maradona for hours before the match — raising their voices even louder after Lazio lost, which set up the chance for Napoli to clinch the Scudetto.
The game had been moved back a day from Saturday on a request from local authorities to maintain public order. But Salernitana, who haven't lost in more than two months, wouldn't let the celebration happen.
But the Napoli fans applauded their team at the final whistle.
"We sense the affection loud and clear in our ears and minds," Spalletti said. "This just extends the enjoyment."
In Milan, Lautaro Martinez scored twice and Romelu Lukaku provided two assists as Inter came back from a goal down to beat Lazio.
Inter defender Francesco Acerbi lost possession to set up an early Lazio goal from Felipe Anderson, with Ciro Immobile also helping out before the Brazilian fooled the defence to gain some space and fire in from the edge of the area.
After numerous chances for Inter, the Nerazzurri finally equalised in the 78th when Lukaku threaded a through ball for Martinez, who scored from the center of the area as he was sliding to the ground.
Lukaku then provided a cross-field pass that Robin Gosens redirected in with an acrobatic volley near the far post — injuring himself in the process.
Martinez scored his second in the 90th after a defensive error.
It was only the second win in seven Serie A matches for Inter, who have reached the Champions League semi-finals and Italian Cup final.
"It was one of our best performances," Inter coach Simone Inzaghi said.
His side moved up to fourth, level on points with fifth-place AC Milan and sixth-place Roma.
In other matches, Sassuolo beat Empoli 2-1 and Cremonese and Hellas Verona drew 1-1.
