Inter stunned 4-1 at Atalanta to end 6-match winning streak
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.
The Portugal forward raced to the corner flag, beckoning all his teammates over to celebrate with him.
"I'm very happy, especially for the team," said Ronaldo, who has been playing and scoring regularly despite facing a rape allegation in the United States. "We played good football, it's never easy to play at San Siro against Milan.
"We showed we're superior, I'm really happy. It's an important win, we're back six points ahead of Napoli. I also scored a goal, I'm satisfied."
Milan slipped to fifth, a point behind fourth-placed Lazio, after seeing its three-match winning run in the league brought to an end.
"We played against a team which have been winning for many years and which every year signs a top player," Milan coach Gennaro Gattuso said. "Our levels are different, maybe the penalty could have changed something but I liked my team, not everything is to throw away.
"Juventus isn't just the strongest team in Italy, it's the most well-built in Europe along with Manchester City and Barcelona. We could have stayed in the match right until the end ... but I never had the feeling we were going to hurt them."
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.
Juventus doubled its tally 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.
Kathryn Mayorga filed a civil lawsuit in September in Nevada claiming Ronaldo raped her in his Las Vegas hotel room in 2009. Police reopened an investigation into the allegation at her request.
Ronaldo has denied any wrongdoing.
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.
Stephan El Shaarawy scored a brace, including a no-look chip shot into the far corner in Roma's 4-1 win over Sampdoria.
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.