The Argentine striker's injury-time winner meant the Manchester side, staring elimination in the face after four minutes, have renewed hope of reaching the last 16.
Aguero goal breathes life into Man City Champions League bid
MANCHESTER // It is part of Manchester City's DNA that they make things difficult for themselves and their inaugural Champions League campaign certainly conforms to the club's traditions.
But so is another essential element of City's identity, a never-say-die attitude, and it was evident on a stirring and ultimately satisfactory night.
Behind in the fourth minute to Cani's strike, City rallied admirably, levelled through Carlos Marchena's own goal and dramatically defeated Villarreal.
Sergio Aguero's injury-time winner meant City, staring elimination in the face after four minutes, have renewed hope of reaching the last 16.
The game mirrored the group, City's initial mishaps leaving them with plenty of work to do.
It was not merely that Villarreal scored on their first attack; it was that the goal was so preventable.
An unusually loose pass from David Silva put Nigel de Jong under pressure. The Dutchman was dispossessed by his compatriot, Jonathan de Guzman.
He picked out Giuseppe Rossi, whose shot was parried by Joe Hart, but only into the path of Cani. He slotted the ball into the net.
It can appear nonsensical to argue a goal came too early, but that is how Villarreal may feel. It left them longer to weather the subsequent storm, wave after wave of City attacks threatening to sink the Yellow Submarines, something they did at the last.
City responded vigorously to their early concession. Aleksandar Kolarov's fierce shot skidded wide while Samir Nasri's volley and De Jong's half-volley just cleared the crossbar.
Nevertheless, it was an indication of Roberto Mancini's concern that Aguero, not deemed fit enough to start, was warming up after 25 minutes.
When the first reshuffle came, however, it was with Gareth Barry introduced in an attempt to liberate Yaya Toure, who was pushed forward. If it was a factor in the leveller, the catalyst was Kolarov. The marauding left-back aimed for Edin Dzeko with his low cross. Marchena got there first but only succeeded in diverting the ball into his own net.
Suddenly, City were rampant. Dzeko, found by Silva, was denied by Diego Lopez. The elusive and influential Toure picked out Nasri who, too, was thwarted by the goalkeeper.
City resumed where they left off after the interval, Dzeko's low volley drawing a terrific stop from the overworked Lopez.
When he was defeated, by a thumping shot from Kolarov, the left-back was offside. That the Serb was so advanced, however, was a sign of his impact.
A spectator for much of the domestic campaign, his rampaging runs made him a constant threat and his vicious free kicks troubled Lopez.
Aguero did arrive with half an hour remaining. Following his mesmerising dribble, Dzeko blazed wide. Yet just when time appeared to be running out, City's Argentines combined crucially. Pablo Zabaleta surged down the right flank and crossed.
Aguero arrived to apply the final touch.
For Villarreal, who had held out for so long, it was cruel. They had done enough to keep Hart occupied. The quicksilver Rossi remained a threat on counter-attack, willing to try his luck from acute angles and Villarreal, belying their poor league form - they only sit 13th in La Liga - showed themselves to be accomplished technicians.
Yet they are almost certain to exit the Champions League. City, in contrast, can yet prosper.