Bud Schwenk made his first appearance in the fourth quarter of the game, substituting for Graham as the game turned into a blowout.
But deep into stoppage time, and with what turned out to be almost the final kick of the game, substitute Aguero arrived at the far post to turn Pablo Zabaleta's cross past Diego Lopez to revive City's hopes of reaching the knockout phase.
Santi Cazorla and Walcott were both off target as the visitors struggled to impose themselves and they were not helped when Mikel Arteta, who passed a fitness test on an injured calf before the game, was substituted before the half-hour.
Blackburn continued to seek a way back into the game and substitute David Dunn shot narrowly wide before a firm header from Tommy Spurr came back off the crossbar.
The recalled Maxi Rodriguez crowned a sweeping passing move to give the visitors a half-time lead, but Blues boss Andre Villas-Boas looked to have changed the course of the game when substitute Daniel Sturridge equalised after the interval.
Warrington saw little of the ball in the first half but they got themselves back into the game when substitute Carvell scored from close range and Ratchford converted to cut the gap to 12 points.
Schemes range from midnight Pizza sales to tiny carnival games substituting the gumballs for regular balls.
Grigory Rodchenkov, the head of the Sochi laboratory during the 2014 Winter Olympics, has said that he managed a very different process, working nightly at the Games to substitute incriminating samples before they were analyzed.
Charades games substitute for movie tickets.
Pope and substitute Hughes wasted opportunities to get the visitors back into the game, but substitute Ashley Vincent was carried off on a stretcher after falling awkwardly when attempting a shot at goal.
