The Spanish champions notched up a 2-0 win in the first leg and although they have dropped four points behind leaders Real Madrid in La Liga, Mascherano feels that no one should doubt their winning mentality.
"We have shown over the past five or six years that we have not lost our appetite and we have continued to win trophies. So far this season we have won the (domestic) Super Cup and we are still fighting in three competitions," the Argentine defender said.
"We now have an advantage but what we need to do is to make the most of that and continue to play our own style which is what we've shown over the years. We have faith in ourselves and need to be true to our style.
"Manchester City normally play an attacking style and I expect them to go out with a lot of forwards now. I know (Sergio) Aguero, I would say he is one of the top five forwards in the world," he added.
"Given the space he can destroy you so we will try and make sure that he has as little space as possible. If you do that then you can make it uncomfortable even for even the best players."
Barca have reached at least the Champions League semi-finals in the last six seasons and it is likely to take something special from City to turn around the tie at the Nou Camp.
Still the pressure is on Gerardo Martino's side whose defeat by lowly Valladolid in La Liga at the weekend was their second in three games.
"I personally have played football in different countries and we have been in worse situations. I know that here the expectations are very high but we are used to dealing with situations like this and we just need to react the right way as we have done before," said Mascherano.
"We are worried mainly about playing well and qualifying for the quarter-finals. We have not been consistent recently. Since January we have done well against top side and also there have been some poor games."
Martino played down the significance Barca's recent defeats.
"The losses have all come from different reasons and I don't think it is down to a lack of motivation," he said.
"The players know what they are playing for but what can happen is like the other day they have a bad match. We made a lot of errors in our build-up play," he added.
Martino also looked to take the pressure off his biggest names, Lionel Messi and Neymar.
"They have not been able to play together that much due to injuries for both of them. At the start of the season they did well together and at the moment there hasn't been a great connection between them but it's not a case of adaption," he said.
"Just because they maybe two of the best players in the world doesn't automatically mean that they are always going to work in harmony together."
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