Mario Manduzkic's first half header was enough for Juventus to beat Roma.
Juventus hung on with Mario Mandzukic's first-half header to beat Roma 1-0 in Serie A on Saturday and clinch the unofficial winter title with two matches remaining before the halfway point.
Juventus, seemingly unstoppable en route to an eighth successive Serie A title, has an eight-point lead over second-placed Napoli, which beat Spal 1-0.
Third-place Inter was 16 points behind Juventus after only drawing at bottom club Chievo Verona 1-1.
Roma's misery continued. It has won only one of its past eight matches in all competitions, piling the pressure on coach Eusebio Di Francesco, whose job may be at risk.
Roma goalkeeper Robin Olsen atoned for last week's errors against Genoa with fine saves but could do nothing 10 minutes from halftime when Mandzukic rose high at the far post to head in Mattia De Sciglio's cross from the right.
Olsen kept Juventus at the bay in the second half, including denying Cristiano Ronaldo twice in quick succession. Ronaldo hasn't scored from open play in four consecutive matches.
He thought he set up Juve's second with some good play on the right side of the penalty area before passing for Douglas Costa to poke home, but the goal was ruled out for a Blaise Matuidi foul on Nicolo Zaniolo.
Napoli prepared for Wednesday's clash against Inter Milan with a narrow victory over struggling Spal.
Napoli dominated and thought it took an early lead but Lorenzo Insigne's effort was ruled out for offside.
The home side found the breakthrough during first-half stoppage time thanks to Raul Albiol's glancing header into the far side of the net from Dries Mertens' corner.
Later, Insigne and Mertens hit the posts.
Sergio Pellissier netted a stoppage-time equalizer to cancel out Ivan Perisic's first goal for Inter in nearly three months.
Mauro Icardi rode a tackle and picked out Danilo D'Ambrosio, who sent in a low cross for Perisic to smash into the roof of the net in the 39th minute.
Both goalkeepers pulled off marvelous saves in the second half while Pellissier sent an overhead kick inches wide.
Inter looked sluggish and the visitor was punished late on as a long ball was knocked on for Pellissier and the 39-year-old striker outsprinted the defenders to chip the onrushing Samir Handanovic.
Chievo finished with a sixth consecutive league draw.
FIGHT FOR FOURTH
Lazio ended a seven-match winless run to leapfrog AC Milan into fourth spot and the final Champions League berth.
Sergej Milinkovic-Savic ended his three-month goal drought to set Lazio on its way to a 3-1 win over Cagliari.
Lazio moved a point above Milan, which lost at home to Fiorentina 1-0.
Federico Chiesa scored for Fiorentina and Milan failed to score for a third successive league match.
Fabio Quagliarella scored for a seventh successive Serie A match, becoming the first Italian to do so in more than 10 years, as Sampdoria won at Empoli 4-2.
Sassuolo drew with Torino 1-1, and Atalanta lost at Genoa 3-1, with Josip Ilicic missing a first-half penalty.
Atalanta ended the match with nine men as Jose Luis Palomino and Rafael Toloi were sent off in the final seven minutes.
Udinese remained a point above the relegation zone after drawing with fellow struggler Frosinone 1-1 as 18th-placed Bologna also drew, 0-0 against Parma.
Frosinone is 19th, five points from Udinese.