The 19-year-old played a pivotal role coming off the bench in helping the Black Cats recover a 2-0 deficit to force an FA Cup third-round replay against Bolton.
Within three minutes of arriving the striker fired home from close range and he continued to look a threat after Gardner had smashed home the equaliser from long range.
"Connor is coming of age now," said Gardner of the 6ft 2ins, 14-stone front man.
"He is getting mentally stronger and he knows where the net is.
"He is an absolute animal and he bullies people and that is what he needs to do because he has a great future ahead of him."
The draw at the Reebok Stadium prevented a third successive defeat for Sunderland.
With their results in the Premier League being more down than up this season Gardner admits their resilience has got them through again.
And he credited manager Martin O'Neill with inspiring the players.
"Bolton went 1-0 up through one of our errors and when they went 2-0 up you thought 'Flipping hell'," he added.
"But I keep going on about the spirit in the camp - and I'm probably boring people - but it's really important to have.
"At half-time we said 'There's 5,000 fans out there, let's give them something to go away with' and it is massively important we are in that hat.
"Things happen in cups which don't normally happen in the league but it's okay because we're still in there.
"We battled and battled and in the end we could have won it comfortably.
"Everyone is behind each other and you could see the gaffer loves the cup and he brings that to the players - everyone loves the cup.
"It comes from the top, the gaffer. He is non-stop, he's always jumping around shouting.
"All you have to do is look at the touchline and see him jumping up and down and it makes you want to dig deep.
"I have been with him for seven or eight years now, having also been at Villa with him, and he is a top-class manager, he is brilliant."
O'Neill, who named only six substitutes because of illness and injury, had suggested before the match his players were tired after a busy December.
But Gardner said that was no excuse and that a cup run, if they could get on one, would take care of itself.
"It doesn't matter how many games you play in the cup, your momentum will get you through it," he said.
"It is hard, don't get me wrong. As a player it is really hard playing seven or eight games in December but that is what we get paid for.
"We can't moan, we just have to get on with it.
"We have a small squad so hopefully the gaffer will bring in some additions in January.
"It is a long season, especially when you stay in the cup, and we need some more players to help us get through the season."