Manchester City's Gael Clichy is shown a red card by referee Felix Brych during their Champions League round of 16 first leg soccer match against Barcelona in Etihad Stadium in Manchester, Feb 22, 2015. [Photo/Agencies]

Dani Alvez clipped the crossbar before the halftime whistle offered stunned City a few minutes to clear their heads.

However, Barca were caught snoozing at the start of the second half and Javier Mascherano had to make a superb tackle to deny Nasri before unmarked City striker Edin Dzeko headed straight at Marc-Andre ter Stegen.

City's endeavour was rewarded when Aguero, whose hat-trick against Bayern Munich in the group stage helped City mount a great escape into the last 16, clipped a shot past ter Stegen after brilliant work from David Silva.

With Clichy off for a second booking, Messi earned a last-gasp penalty when he was bundled over by Zabaleta but his effort was saved by Hart and the Argentine then missed an open goal with a diving header from the rebound to leave City alive.