Serie A leaders Juventus beat Parma 2-1 to extend their lead at the top of the standings to four points on Sunday and remain firmly on course for a record-extending ninth straight league title.
Cristiano Ronaldo netted once in each half to continue his run of scoring in seven consecutive league games.
The Portugal ace has 16 goals for the season and only trails Lazio's Ciro Immobile (23) in the race for the golden boot. Ronaldo's brace takes his tally to 432 goals in Europe's top five leagues, one behind all-time record-holder Lionel Messi, who scored for Barcelona on the night.
Juventus have 51 points after 20 rounds, with Inter on 47 and Lazio on 45 with a game in hand.
A deflection from Matteo Darmian late into a sluggish first half helped Ronaldo open the scoring.
Andreas Cornelius headed in a corner to draw visiting Parma, seventh on 28 points, level in the 55th minute but Juve restored their lead just three minutes later.
Argentine Paulo Dybala raced down the right and rolled the ball across for Ronaldo to sidefoot home his 11th goal in his last seven league matches.
"The match was difficult because Parma is a good team and put us in difficulty. I'm happy to have helped the team with two goals, but what's important always is the three points at the end," Ronaldo said.
"Lazio won, Inter drew and we couldn't allow ourselves not to make the most of that important advantage."
Inter Milan slipped further behind in the race for their first title since 2009-10 after being held to a 1-1 draw at struggling Lecce.
Promoted Lecce, who also held Juventus to a 1-1 draw in October, are one point clear of the drop zone as the league resumes after its halfway winter break.
The Nerazzurri had to wait for the 20-year-old Alessandro Bastoni to come on and head home the opener in the 72nd minute.
Hosts Lecce levelled five minutes later as substitute Zan Majer squared to see his captain Marco Mancosu get the better of Bastoni.
Roma clinched a 3-1 win at second-bottom Genoa to go fourth on 38 points and move into the last Champions League place.
In the day's opener, Croatian substitute Ante Rebic scored a double as AC Milan rallied to a late 3-2 victory at home to Udinese and move up to eighth.
Brescia and visiting Cagliari drew 2-2 with braces from Ernesto Torregrossa and Joao Pedro, with Mario Balotelli receiving his marching orders for the 18th-placed home side on 81 minutes, while Bologna drew 1-1 with Verona.
On Saturday, third-placed Lazio pummelled visiting Sampdoria 5-1, Sassuolo beat Torino 2-1 and Fiorentina won 2-0 at Napoli.
Fifth-placed Atalanta host bottom of the table SPAL on Monday.