Reigning champion Inter Milan missed an opportunity to retake the Serie A top spot following a 2-0 home defeat against giant-killer Sassuolo on Sunday.
First-half strikes from Giacomo Raspadori and Gianluca Scamacca gave Sassuolo an impressive win at the San Siro which left Inter two points behind Milan, who had opened the door for their local rivals with Saturday's draw at bottom side Salernitana.
It was the latest triumph for Sassuolo at one of Italy's big three after also winning at Milan and Juventus this season.
"We created a lot, and we conceded a fair amount too but we know we have quality so we faced them head-on," said Sassuolo coach Alessio Dionisi to DAZN.
"That's what we wanted to do and we were rewarded for it."
The ball is now in Napoli's court in an exciting three-way title race as Luciano Spalletti's side, who sits a point behind Inter in third, can move top on goal difference with a win at Cagliari on Monday evening.
Simone Inzaghi's side was missing midfield lynchpin Marcelo Brozovic and starting center back Alessandro Bastoni to suspension and looked tired after the midweek defeat to Liverpool.
"We'll try to recover some physical and mental energy. We're still in the fight, there are still 13 matches left and we want to keep going," said Inzaghi.
Inter's current fragility was exposed in the eighth minute when after Berardi pinched the ball from Hakan Çalhanoğlu he fed Raspadori who hit a low shot which squirmed home past Samir Handanovic.
And Scamacca, who is hotly tipped to move to Inter alongside teammate Davide Frattesi in the summer, stunned the home fans when he drifted into the area unmarked and headed home his 10th Serie A goal of the season from Hamed Traore's inswinging cross.
The away side could have easily been three goals up at the break, as Domenico Berardi thumped a beautiful shot off the bar in the 38th minute.
However, Inter only had itself to blame for not having made more of a game of it, as a wave of second-half pressure brought enough chances to at least escape with a draw.
The worst offender was Lautaro Martinez, who left Inter fans opened-mouthed in the 72nd minute when he somehow poked wide with an open goal at his mercy.
Earlier Krzysztof Piatek helped Fiorentina fans forget Dusan Vlahovic by firing his new team firmly into the Champions League race with the only goal in a 1-0 win over off-form Atalanta.
Polish international Piatek netted a well-taken fifth goal in six appearances in all competitions since returning to Italy from Mainz in January to move Fiorentina up to seventh, five points behind fourth-placed Juventus.
Vincenzo Italiano's side also has a game in hand on Juve, whose 1-1 draw with Torino on Friday had given Atalanta, who on Friday announced that a group of American investors had bought a sizable stake in the club, the chance to move up one place into fourth with a win in Florence.
However, it offered very little once Ruslan Malinovskyi was denied a leveler shortly after going behind for Hans Hateboer straying marginally offside when making a run and being judged to have interfered with play.
That decision so enraged coach Gian Piero Gasperini that he was sent off and refused to speak to media afterward, while the club posted an image of the move highlighting Malinovskyi's onside position with the message "judge for yourself."
Also in the Champions League mix are Lazio, who shorn of Serie A's leading scorer Ciro Immobile, Luis Alberto and Lucas Leiva could only draw 1-1 at Udinese.
Maurizio Sarri's side would have moved to within two points of the top four with a win but couldn't add to its tally after Felipe Anderson struck on the stroke of halftime to equalize Gerard Deulofeu's early opener for the host side.
