PHOTO: AFP
Not to be outdone, however, Napoli's Arkadiusz Milik also bagged a brace with a 3-2 home win against Bologna to keep the pressure on the champions.
Ronaldo-powered Juventus have achieved a record number of points before the three-week winter break with 53 from 19 games.
Napoli are nine points behind in second, with Inter Milan a further five adrift in third, days after their clash at the San Siro was overshadowed by the death of a supporter with Napoli defender Kalidou Koulibaly targetted by racist chanting.
Koulibaly was suspended for Saturday's game but fans showed their support in his San Paolo stadium by wearing masks with the defender's face and holding up banners saying: "We are all Koulibaly".
Ronaldo rescues point for 10-man Juventus
Dries Mertens sealed victory two minutes from time after Bologna battled back twice to level Milik's goals on 15 and 51 minutes.
"It was important to end the year on a high and it wasn't at all easy," said Juventus coach Massimiliano Allegri after a game in which the video assistant referee played a key role.
Two penalties were decided by VAR with Sampordia also having a late equaliser ruled out.
Ronaldo curled in the opener after just two minutes in Turin, adding a second from the spot on 65 minutes, to go top of Serie A's scoring charts on 14 goals.
Fabio Quagliarella pulled the Genoa outfit level with a penalty on 33 minutes, before Riccardo Saponara's late equaliser was ruled offside.
Sampdoria coach Marco Giampaolo, dismissing Ronaldo's penalty as "a gift," adding "that Saponara goal should never have been cancelled".
"For me, morally, the game was 2-2."
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