City produced an imperious performance on Wednesday to dismantle their Championship opponents in a game that was in stark contrast to the 1-1 draw in the first encounter at Ewood Park earlier this month.
Spain striker Alvaro Negredo put City in front with a powerful header in first-half injury time before doubling his side's advantage midway through the second half with a cool finish that marked his 21st goal of the campaign.
Edin Dzeko then added a third for last year's beaten finalists, who were handed a further boost in the second period as Sergio Aguero came off the bench to find the net in his first appearance since suffering a calf injury against Arsenal last month.
And the gloss on a scintillating display was applied in the closing stages, Dzeko turning home his second as City kept hopes of a quadruple-winning season very much alive.
However, City would have taken the lead had Negredo or Fernandinho been able to make contact with Jesus Navas' low delivery across the face of goal.
But Manuel Pellegrini's men finally broke the deadlock just before the interval as Negredo headed home Fernandinho's right-wing cross with a powerful close-range header.
And Negredo all but ensured City's place in the fourth round within two minutes of the restart, the Spaniard latching on to an excellent pass from Kolarov to lift the ball over Eastwood and net his 16th goal in 12 games at the Etihad Stadium.
Blackburn were made to pay for King's profligacy in the 67th minute as Dzeko lashed home a Navas pull back to further illustrate City's dominance.
