The Frenchman, unnerved by the occasion, served to get Real Madrid back in the tie before going on to reach the final in the second leg in the Spanish capital
Benzema is the favourite for the Ballon d'Or, and admits that he had long been thinking about taking such a penalty.
"I had been practising the 'Panenka' for a long time and I was just waiting for the right moment, in a match like that, where there is a lot of pressure," he told RMC Sports.
"It's this kind of pressure that allows you to do things like that, at least for me."
Indeed, there are few moments of greater tension than a Champions League semi final away from home and with your team losing.
Madrid's penalty in Manchester came when City were 4-2 up and it was all down to Benzema keep his side in the tie.
The Panenka-style penalty even brought many City fans to their feet to applaud the French star's technique and audacity.
It should also be remembered that Benzema had seen two penalties of his saved by Sergio Herrera of Osasuna the week before, adding further pressure to his kick.
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