Napoli also had to fight harder to get points in last night's match against Cagliari as a team in the relegation zone, even though on paper Napoli should have won easily even if it was only one goal. But what happened was that Cagliari could take the lead first and Napoli could just score a goal in the last minute of the match and indeed, Napoli should be more focused against Barcelona next but with Inter getting a defeat Napoli should be more motivated to overtake Inter in the standings.
Napoli are in the race with two Milan clubs. They don't fall behind Milans too much but they don't have many good substitution players like Inter Milan or AC Milan. So if they get luck enough till the end of season without injury or long absence of their key players, they can fight for Scudetto and even might win it. If their key players get troubles and can not contribute in a few matches, Napoli can be out of the competition.
I think AC Milan still lucky with rival result match getting where Inter Milan defeated by Sassuolo then failed get three points, the same situation with Napoli exactly have chance to lead fixture standing a week but last night draw with Cagliari. Now Milan can focus on the next match still hope how to missing failed again get three points. Still have competitive for Milan, Inter and Napoli how to get scudetto but only Napoli looks difficult against on next week faced with Lazio. Milan vs Udinese looks not heavy how get three points and Inter Milan vs Genoa should easy to win.
To win a big competition like Scudetto, lucky is not enough. They will have to fight hard, need luck and support from unknown factors from referees to weathers, etc. AC Milan are on their good movement to challenge Inter Milan for the trophy but the season is on and lots of match ahead. They will have to play towards the end of season with their best and without hope that Inter Milan will lose so many points.