Kylian Mbappe and Erling Haaland are the only players to have netted in four games in a row at a younger age than 20-year-old Spain international Torres, who scored in the 12th minute, adding to his strikes against Porto and Marseille for City this term and against Atalanta for Valencia last season.
City went into this game unbeaten in seven matches in all competitions and could have been out of sight by the time the Greek champion began to put City under pressure in the second half.
But substitutes Gabriel Jesus and Joao Cancelo scored late on to clinch a result that extends City's group stage streak to 14 games without defeat, and manager Pep Guardiola will be pleased with their form as he aims to take City beyond the quarter-finals for the first time in his reign.
Torres met a City corner with a sublime backheeled shot that flew narrowly wide after six minutes.
City's recent signing went one better six minutes later, playing a one-two with Kevin De Bruyne before sliding a low shot through the legs of goalkeeper Jose Sa to put the hosts in front.
Guardiola's men continued to create the better chances and Raheem Sterling put the ball in the net, only to have his close-range effort ruled out for offside.
A poor pass by Phil Foden afforded Mathieu Valbuena a shot at goal early in the second half but he fired narrowly wide under pressure from John Stones.
Youssef El-Arabi tested Ederson with a shot from just inside the box as City found themselves pinned back again, and Jose Holebas later blazed wide.
But De Bruyne played in Jesus nine minutes from time and the Brazilian lashed the ball home from an acute angle, before Cancelo's carefully placed shot found the bottom corner from just outside the box to wrap up the win.