Napoli announced their proposal for the Serie A title with Sunday's 2-1 victory at AC Milan which maintained their league lead, while the conflicts at Juventus deepened following a embarrassing defeat at Monza.
Spalletti's team sit top of the pile on goal difference from Atalanta, 1-0 winners at Roma, and three points ahead of Milan who sinked down to fifth after their first defeat of the season.
Milan were the more threatening team in the first half and would have taken a 13th minute lead had Alex Meret not brilliantly tipped Olivier Giroud's shot onto the bar.
However shorn of the suspended Rafael Leao, Milan lacked their usual cutting edge, and combined with a couple of infortunate incidents of players getting in the way of each other's chances denied Milan a deserved advantage at the break.
They were punished 10 minutes after the break following a decision which enraged Milan, Maurizio Mariani pointing to the spot for a foul on Khvicha Kvaratskhelia by Sergino Dest and Politano striking the penalty under Mike Maignan.
Giroud dashed the angry crowd what they wanted but his fourth league strike of the season was all his France teammate Theo Hernandez's work, a superb burst down the left flank and cut back making it easy for the veteran strike to level the scores.
However while Milan pushed for a winner Simeone hit them with a sucker punch, meeting Mario Rui's flighted pass with a perfect header.
Milan responded again but after Pierre Kalulu somehow hit the bar from Giroud's flick on with four minutes remaining Napoli held out for a potentially huge three points.
Atalanta reclaim lead
Atalanta are level with Napoli after Giorgio Scalvini's beautifully hit low strike 10 minutes before the break at the Stadio Olimpico earned them the three points.
Gian Piero Gasperini's side are a point ahead of Udinese, who beat Inter Milan 3-1 in Sunday's early match to win their fifth match on the bounce.
Roma, who lost Paulo Dybala to injury in the pre-match warm up and were wasteful in front of goal, were livid 10 minutes after the break when referee Daniele Chiffi didn't give the hosts a penalty for Caleb Okoli yanking at Nicolo Zaniolo's shorts to the point that his underwear was visible.
"I need to change what I tell me players, I have to tell them to not to stay on your feet... be a clown like many who dive like they're in a swimming pool do in this league," said Mourinho to DAZN after being sent off for his protests.
Juve in crisis
Juventus were in trouble before Sunday, and the boos from the stands after their midweek defeat to Benfica were replicated from the away end at the U-Power Stadium after a devastating 1-0 loss.
Monza owner and one-time Milan patron Silvio Berlusconi celebrated after Christian Gytkjaer netted their historic winner 15 minutes from the end and increased pressure on Juve to sack coach Massimiliano Allegri.
Allegri was not on the bench after being sent off at the end of last weekend's home draw with Salernitana, and Angel Di Maria said the defeat was his fault after being sent off for elbowing Armando Izzo five minutes before the break.
Fans are placing the blame firmly with the man who won them five league titles for their team's dismal results and performances which have left them eight and 10 points behind the leading duo.
However before the match Juve CEO Maurizio Arrivabene said it would be "crazy" to sack Allegri, under contract until 2025 on a reported salary of eight million euros a year, and there has been no indication that he is about to be let go.
Monza are still in the relegation zone but move above Sampdoria and Cremonese, thumpd 4-0 by Lazio, and are a single point behind 17th-placed Verona following their 2-0 defeat at Fiorentina.
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