The 36-year-old striker found the net with a header, a right-footed penalty and a left-foot shot and celebrated by pointing to his ear in an apparent response to recent criticism.
The Italian champions and their Portuguese talisman were under pressure to perform after suffering a Champions League last-16 elimination against Porto on Tuesday.
They enjoyed a comfortable win despite Giovanni Simeone’s second-half strike for the hosts and are now third with 55 points, 10 behind leaders Inter Milan with a game in hand.
Ronaldo declined to give a post-match interview when asked at full-time and Juve captain Giorgio Chiellini faced the cameras instead.
“Our strength has always been to respond on the pitch and we did that today, Cristiano above all,” he told Sky Italia.
“We played like Juve and as a team, with our strengths and weaknesses. But with this main ingredient we can finish the season well, we’ll see where we are by mid-May.”
It was Cagliari coach Leonardo Semplici’s first defeat since taking over in February and left his side in 17th place on 22 points, two clear of the relegation zone.
Ronaldo came in for widespread criticism and was linked by the media with a possible close-season departure from Juve after his disappointing display against Porto, who knocked the Turin club out of Europe on away goals following a 4-4 aggregate draw.
But the Portuguese forward was fired up for the trip to the Sardegna Arena and quickly made his mark by powering in a header from a corner after 10 minutes, a goal that means he has now scored in all 18 stadiums he has visited in Serie A.
Ronaldo was booked for catching goalkeeper Alessio Cragno in the face with a high boot as they both went for a cross, and the striker was then brought down in the box by the keeper and smashed home the resulting penalty in the 25th minute.
He soon had his third goal as he performed a trademark step-over before hammering a shot past Cragno to mark the second fastest hat-trick of his career, after the treble he scored in 20 minutes for Real Madrid against Espanyol in September 2015.
Cagliari pulled a goal back in the second half when Simeone fired in a low shot and Ronaldo had a big chance to score his fourth with the last kick of the game when one-on-one with Cragno but the keeper denied him with an excellent block.
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