Mannone, who came on for the injured Keiren Westwood in the 1-0 defeat at Hull City in early November, has started Sunderland's past four matches.
He has conceded just three goals in that run and, following the weekend's 0-0 draw at Aston Villa, the summer signing feels Sunderland are looking more solid.
"As I said a few weeks ago, I thought everything changed around at Hull when we kept a clean sheet nine against 11," Mannone is quoted in the Evening Chronicle. "That was massive in our mentality.
"You can tell, even at Stoke last weekend and at Villa on Saturday, we are much more solid now.
"We do not want to give things away cheaply. It is massive we have stopped conceding goals.
"The manager came in and gave us this mentality of keeping clean sheets. It is really, really important.
"You cannot believe how much confidence it gives to the team because when you feel solid you can play your game.
"If you don't, you start giving the ball away and teams are coming at you."
Sunderland have picked up just two points away from home so far this season and Mannone feels wins are needed on the road to boost the club's hopes of staying in the Premier League.
Mannone added: "I thought we did really well on Saturday. We were unlucky because with the chances Emanuele [Giaccherini] and Fabio [Borini] had we could have taken the three points.
"We need to pick up some wins away. It will be so important for survival."