Jose Mourinho's side were on the verge of crisis after a dreadful start to La Liga and the Portuguese coach had launched a stinging attack on his players in a bid to stun them into life for their opening game in Europe's elite club competition.
Ronaldo's revelation two weeks ago that he was feeling "sad" for professional reasons and his refusal to celebrate goals had not helped but Mourinho's rallying call appeared to have the desired effect as Real stormed back to break City hearts.
The English champions were on the verge of pulling off a stunning smash and grab raid against the nine-times European champions at the Bernabeu, twice taking the lead in the second-half through substitutes Edin Dzeko and Aleksandar Kolarov.
Roared on by fans desperate for a return to winning ways, Real equalised first through Marcelo and then as late as the 87th minute when substitute Karim Benzema stroked the ball into the net just two minutes after Kolarov's strike.
The stage was set for the world's most expensive player and Ronaldo danced in from the left and unleashed a powerful shot that flew into the net under City goalkeeper Joe Hart.
The ecstatic Real fans celebrated as if their team had just won the 10th European crown that has eluded them since 2002 and Mourinho, fists pumping, performed a celebratory knee slide onto the pitch from his technical area.
"I celebrate when I have to celebrate," a jubilant Ronaldo, who has now scored 151 goals in 151 appearances for Real, told Spanish television.
"The match was very important for us and we are back in the fight," added the Portugal forward whose Champions League tally of 39 puts him level with former Chelsea striker Didier Drogba.
The clash in the Spanish capital was a contest between Europe's biggest spenders over the past four seasons and a thrilling encounter lived up to the pre-match hype.
Mourinho sprung several surprises in his starting lineup, leaving out experienced Spain centre-back Sergio Ramos and replacing him with French 19-year-old Raphael Varane.
He also handed a debut to defensive midfielder Michael Essien, who joined from Chelsea last month, and left playmakers Mesut Ozil and another new signing, Luka Modric, on the bench.
City's Roberto Mancini fielded an unambitious formation with Carlos Tevez ploughing a lonely furrow up front with David Silva and Samir Nasri on the flanks in front of defensive midfielders Yaya Toure, Gareth Barry and Javi Garcia, a former Real player.
Real were under pressure to produce a convincing European performance after losing two and drawing one of their opening four La Liga games and made their intentions clear early on when Ronaldo forced two fine saves from Joe Hart.
City barely had a sniff of goal in the first half, while Real striker Gonzalo Higuain fluffed two clear chances, one when he was clean through with only Hart to beat and the other when he volleyed over from close range.
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