City were beaten at the Etihad in a lively first leg on Tuesday night but they stood firm after Clichy was sent off with Hart keeping the score to 2-1 by shutting out Messi’s spot-kick in injury-time.
Clichy will be suspended for the return leg at the Nou Camp but he remains upbeat about his side’s chances of making the quarter-finals.
The Frenchman said: “We always say you have to look for positives and I think this save was a massive one.
“I am not talking about the quality of Joe – because he is one of the leaders in the dressing room and on the pitch – but this save could be the turning point.
“I am not saying it’s going to be easy, and you cannot say this save is going to make us win the game.
“But, for sure, 2-1 is a different score to 3-1 and we have to look forward. We have the quality to do something and we are going to try our best and hopefully get something out of the game at the Nou Camp.”
City were overrun in the first half and conceded twice to a Luis Suarez double, but the hosts hit back with a fine Sergio Aguero strike and were left scrapping for their lives after Clichy was dismissed for two bookable offences.
His second yellow card, for a high challenge on Dani Alves in the 73rd minute, seemed harsh and Clichy, who was slow to leave the field, felt he was unlucky.
The 29-year-old said: “If you play by the rules, they are probably two yellows, but I have done two fouls during the game, and I wouldn’t even call them big fouls.
“So probably after the first booking, if I had made four or five fouls and the ref is saying, ‘Okay, the sixth one is enough’ that would have been fair. But it was only my second one, and they made some fouls as well, probably worse than mine, and didn’t get booked.
“Those fouls in England are not bookings, but we were in Europe. That’s the way it is and I can’t complain because, by the rules, it is probably two bookings.
“At the end they got a penalty. It was probably a penalty, but it was still a big decision. But the game is not over.”