Ronaldo took center stage again after a relatively quiet international break with one goal in three games for Portugal, scoring in the 38th minute for his side to find the back of the net in the fifth successive league match.
The 35-year-old forward doubles his side’s advantage with a brilliant strike at the far post to take him to eight league goals for the season, in just four starts.
Watch the match highlights below
Ronaldo also set up two opportunities as Juventus threatened to score again but poor finishing denied the hosts from adding to their tally.
The win means Andrea Pirlo’s unbeaten side close the gap to leaders AC Milan to one point, with Milan playing at Napoli on Sunday.
Having won four of their previous five games in all competitions, Cagliari showed plenty of confidence in the early stages, with Juventus looking a little bit shaky having won just three of their last seven before the international break.
However, Ronaldo looked sharper than anyone on the pitch despite having to recover from COVID-19, then an ankle injury, before traveling to play for his country.
The Portuguese first goal was a trademark one as he cut inside twice before driving a low shot into the net, but the second was even better, flicking home after adjusting to meet a diverted ball which was behind him.
Crotone 0-2 Lazio: Immobile made history as he helps Lazio move up to fifth
Ciro Immobile helped Lazio to a 2-0 away victory at Crotone to become the Italian side’s joint second top goalscorer in Serie A history in wet conditions on Saturday.
Violent storms and flooding in Calabria threatened but the match was allowed to continue after the pitch passed an inspection.
Immobile scored in the 21st-minute through a header to move onto 107 Serie A goals for Lazio, alongside Giuseppe Signori.
The visitors wrapped things up and secured all maximum three points in the second half as the rain subsided and Joaquin Correa continued his sterling form in front of goal by squeezing in another goal for Lazio’s second.
The win stretches Lazio’s unbeaten run to seven in all competitions as Simone Inzaghi’s side moved up to fifth in the Serie A standings, while Crotone remains at the bottom.
Elsewhere on Saturday, Atalanta was held to a 0-0 draw at Spezia.