Gardner told PA Sport: "In the second half against Newcastle we showed just how good a team we actually are and we battered them. It showed our desire to succeed whereas two or three seasons ago in the same position, Villa would have folded.
"Now Martin O'Neill is here, Villa are bouncing back all over the place and never give up. It's happened a few times this season after we have gone a goal down.
"At half-time against Newcastle the lads came in a bit down, but the gaffer just said 'okay, we've had a bad first half but we will win this game easily.'
"He said 'look where we are in the league, we can qualify for the Champions League next season, now go out there and get a result.'
"The atmosphere in the dressing room before we went back out was unreal. Everyone got so psyched up. It was amazing and we worked our socks off and got a result."
Gardner added: "The gaffer's middle name should be 'belief' because, if we were 6-0 down he would make us think we could win 7-6. He is just unbelievable and all credit to him.
"To give the players so much confidence and self belief can only help us in our bid to get into Europe."