Torino moved three points above the relegation zone, with a game in hand.
Ronaldo, who just turned 36 one day before, marked his birthday with an opening goal in the 12th minute.
He has made 27 appearances for the Blues so far, including four this season, most recently as a substitute in the FA Cup third-round win over Morecambe earlier this month.
Ibrahimovic converted a first-half penalty and doubled his tally early in the second period
With Paulo Dybala injured, Andrea Pirlo on Saturday evening opted for Ronaldo to partner Alvaro Morata upfront, while Rodrigo Bentancur pulled the strings in the midfield, reports Xinhua news agency.
French defender Theo Hernandez's brace rescued a point at the death for AC Milan who came from two goals down to draw 2-2 against Parma in the San Siro.
"Ronaldo carried out a check with a diagnostic test (swab) for Covid-19. The exam provided a negative result," the Italian champions said in a statement.
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