Adel Taarabt beat visiting keeper David Marshall, but saw his shot hit the post from 25 yards and Cardiff were relieved to see the ballricochet for a goal-kick.
The Argentine laid off to Nasri, who tried to play a 1-2 with Aguero, only for the ball to ricochet back to the Frenchman off Cesar Azpilicueta and he calmly slotted it past Cech.
However, then came Forde's sending off with the ball appearing to ricochet off his own boot to hit his hand as he charged out of his own area in an attempt to avert the danger.