The goal was Ronaldo's first at the San Siro in six matches.
MILAN (AP) – Cristiano Ronaldo ended his San Siro hoodoo to help Juventus to a 2-0 win after AC Milan forward Gonzalo Higuain missed a penalty against his former team on Sunday.
Higuain left Juventus in the offseason following the signing of Ronaldo and he had a nightmare game as he was also sent off seven minutes from time for dissent after being booked for a foul on Medhi Benatia.
Mario Mandzukic scored early on and Ronaldo sealed the result nine minutes from the end as Serie A leader Juventus won at Milan to restore its six-point advantage over second-placed Napoli, which beat Genoa 2-1 on Saturday.
It was Ronaldo's first goal in six matches at San Siro, having previously played at the iconic stadium for Manchester United and Real Madrid.
The Portugal forward raced to the corner flag, beckoning all his teammates over to celebrate with him.
Milan slipped to fifth, a point behind fourth-placed Lazio, after seeing its three-match winning run in the league brought to an end.
Juventus was looking to bounce back from Wednesday's shock 2-1 defeat at home to Manchester United and welcomed back Mandzukic from injury.
It took the Croatia forward less than eight minutes to break the deadlock, running in at the back post to head in Alex Sandro's cross from the left.
There were few clearcut opportunities in a cagey match but Milan was awarded a penalty shortly before halftime when Benatia blocked Higuain's effort with his hand.
Higuain stepped up but his spot kick was weak and Juventus goalkeeper Wojciech Szczesny managed to tip it onto his right post.
Paulo Dybala almost doubled Juve's lead in the second half but his free kick came off the outside of the upright.
Juventus did get its second goal nine minutes from time. Joao Cancelo's shot was beaten away by Milan goalkeeper Gianluigi Donnarumma but only into the path of Ronaldo, who blasted into the roof of the net from close range.
Inter Milan was thoroughly outclassed in a 4-1 loss at regional rival Atalanta for its first Serie A defeat in nearly two months.
The loss left Inter third, nine points behind Juventus.
Inter had won six straight and hadn't lost since falling 1-0 at home to Parma on Sept. 15.
''We weren't ready for this match,'' Inter coach Luciano Spalletti said. ''Our standards dropped. After a series of victories it doesn't mean things run automatically. We need to work on that.''
Hans Hateboer gave Atalanta an early advantage with a tap-in and the hosts wasted numerous other chances - including an attempt off the post - to add to the lead before the break, as Inter appeared worn out following a 1-1 draw with Barcelona in the Champions League.
Mauro Icardi equalized with a penalty two minutes into the second half following an Atalanta hand ball but Gianluca Mancini restored Atalanta's lead after the hour mark with a header from Josip Ilicic's free kick.
Berat Djimsiti scored with a header on another set piece from Ilicic, and Inter was then reduced to 10 men when Marcelo Brozovic picked up his second yellow card.
Papu Gomez completed the scoring with a long, curling shot that left Inter goalkeeper Samir Handanovic motionless.
With its fourth straight win, Atalanta is eighth.
Stephan El Shaarawy scored a brace, including a no-look chip shot into the far corner in Roma's 4-1 win over Sampdoria.
The victory ended a three-match winless streak in Serie A for Roma.
Juan Jesus had given Roma an early lead then Patrik Schick doubled the advantage against his former club.
Gregoire Defrel pulled one back for Sampdoria before El Shaarawy converted a rebound to restore the three-goal advantage.
Last-place Chievo Verona drew 2-2 with Bologna to earn its first point since former Italy coach Gian Piero Ventura was hired a month ago.
Empoli, which was playing its first match under new manager Giuseppe Iachini, beat struggling Udinese 2-1.
In its last seven matches, Udinese has lost six and drawn one, putting the job of coach Julio Velazquez at risk.