The Belgian established himself as O'Neill's No1 last season.
"The little things he says to the players week in, week out make us believe in ourselves even more and that makes a huge difference on the pitch."
Mignolet also told saf.com: "The manager makes sure the players train well during the week but also get their rest.
"When you come in before a game and the manager starts speaking, everyone listens and knows how important the game is and that we have to perform.
"When taking over the most important thing for a manager is winning points and he has done that."