Milan - Paulo Dybala and Blaise Matuidi scored early as Juventus extended their perfect start to their Serie A title defence to six games on Wednesday with a 2-0 win over Bologna, as Roma ended their losing streak with a 4-0 success over promoted Frosinone.
"We made some mistakes at the end of the match and we were sometimes vulnerable," said Juventus coach Massimiliano Allegri.
"On Saturday it's a head-to-head with Napoli and it'll certainly be a great game. I don't have a line-up in my head right now, as on Friday in training we'll see everyone together and decide."
Lazio are third, a further three points adrift, after their fourth win on the trot 2-1 against Udinese ahead of this weekend's Roman derby against Roma.
Roma, meanwhile, eased the pressure on under-fire coach Eusebio Di Francesco achieving their first three points since their season-opener against Torino over a month ago.
"This is a new beginning for us, a new season has started," said Di Francesco.
In Turin, Dybala got a rare start up front alongside superstar Cristiano Ronaldo and lashed home his first goal of the season after 12 minutes in the Allianz Stadium.
The Argentine had initially teed up Matuidi but Lukasz Skorupski cleared the Frenchman's effort before Dybala acrobatically turned the ball in himself.
Five minutes later World Cup winner Matuidi got his chance to add a second following a Ronaldo cross, with the Portuguese forward having a shot cleared off the near post by Skorupski.
Ronaldo - who missed out on the FIFA's best player of the year award this week - fired just wide five minutes from the whistle when he picked up Dybala's through ball.
In was the first of three games in Turin within the space of a week for Juventus, who after Napoli at the weekend, host Swiss club Young Boys in the Champions League next week, after winning their opener against Valencia.
Carlo Ancelotti rotated his squad completely with nine changes ahead of the weekend game in Turin and hosting Liverpool in the Champions League.
And it paid off with a third straight league win with Lorenzo Insigne opening after four minutes in Naples with a second-half brace from Polish forward Arkadiusz Milik keeping the pressure on Juventus.
"We were very fresh because I changed them all, and the initial rhythm determined the final result," said Ancelotti.
Lazio, meanwhile, continued their promising start with Francesco Acerbi and Joaquin Correa scoring in the space of five minutes just after the hour mark.
Bram Nuytinck pulled one back in Udine with an overhead kick ten minutes from time.
Simone Inzaghi's side, who lost their opening two games to Juventus and Napoli, can head confidently into the Roman derby against Roma.
In the Stadio Olimpico, Turkish winger Cengiz Under set the tone after just two minutes for Roma with a sensational run from his own half to lash into the goal from a distance.
Javier Pastore's back heel flick gave Di Francesco's side a second just before the half hour mark with Under then setting up Stephan El Shaarawy for the third minutes later.
Luca Pellegrini came off the bench for his Serie A debut, to set up Aleksandar Kolarov for the fourth three minutes from time.
Roma are tenth with eight points, with Frosinone second from bottom having conceded 16 goals this season.
"This is a starting point. It was important to rediscover our confidence and prepare well," said the Roma coach whose side host Czech club Viktoria Plzen in the Champions League next week, having lost their opener to holders Real Madrid.
Inter Milan moved towards the top of the table with a 2-1 win over Fiorentina on Tuesday, with AC Milan playing at Empoli on Thursday.