Ronaldo struck for the fifth consecutive league game as the champions bounced back from their Italian Super Cup defeat by Lazio to move ahead of Inter Milan who play Napoli later Monday.
“I’m happy with this first (league) hat-trick. But the important thing is the team, which played very well,” said Ronaldo, who brought his league tally to 13 goals in 15 games this season.
“We had to win today and put pressure on Inter.”
Cagliari held off Maurizio Sarri’s Juve early on, but the second half was all one-way traffic with 34-year-old Ronaldo breaking the deadlock just after the interval.
The Portuguese striker added a second from the penalty spot on 67 minutes then set up Gonzalo Higuain who came off the bench to strike a third nine minutes from time, before completing his hat-trick a minute later.
Juve are three points ahead of Inter in the table with Antonio Conte’s side travelling to eighth-placed Napoli looking to keep pace with the eight-time defending champions.