Mario Mandzukic’s header earned Juventus a narrow victory over Inter Milan and extended their Serie A lead to 11 points, at least until Saturday.
The Croatian striker pounced to meet Joao Cancelo’s second-half cross after Inter missed a host of good chances.
Before the break, Roberto Gagliardini hit the post with a scuffed shot, while Matteo Politano failed to punish Blaise Matuidi’s error just after half-time.
Napoli can narrow the gap on champions Juve when they play Frosinone.
Carlo Ancelotti’s second-placed side face the 19th-placed Canarini at 14:00 GMT on Saturday.
Juve’s Derby d’Italia victory means they equal the best ever start by a team after the first 15 games of a season in Europe’s top five leagues of England, Italy, Spain, France and Germany.
They have matched French champions Paris St-Germain’s return of this season, with 43 points.
Inter remain third in the table, now 14 points behind Juve, after a match they might have won.
Juve have won the past seven Serie A titles, are undefeated in the league this season and have not lost at home in the league since April, but they were twice exposed and left unpunished by Luciano Spalletti’s side.
After good hold-up play by Mauro Icardi, Gagliardini failed to make a decent connection when he only had Wojciech Szczesny to beat, the ball striking the base of the post and bouncing back to the Juve keeper.
Politano appeared to panic when presented with a golden chance to score from inside the box after Matuidi gave the ball away.
And in injury time, substitute Lautaro Martinez drilled wide with Inter’s final chance, snatching at an opportunity that came from Cancelo’s poor clearance.