The game swung Cagliari's way in the 38th minute when Nandez intercepted a poor back pass and appeared to have a clear run on goal.
He was brought down by Tommaso Augello, who was initially given a yellow card which was changed to a red after a VAR review.
Cagliari went ahead three minutes after halftime when Joao Pedro ran into Lorenzo Tonelli and the referee awarded a penalty which the Brazilian converted himself for his fifth goal of the season.
The Sardinians thought they had added a third when Riccardo Sottil had the ball in the net but it was disallowed for offside following a long VAR review.
The result left both sides with 10 points from seven games.