Wallis debuted for the Bulldogs in last week's loss to Fremantle.
But with the game on the other side of the country and being forced to wear the green substitute vest for the first three quarters, Wallis only got a taste of life as an AFL player with three handballs in his one and only quarter.
This week was different as he started in the forward line in front of more than 50,000 people against the competition's best team.
Wallis said it was a much different build-up second time around.
"I was definitely nervous but I was excited because I didn't get a full game last week so I was told early in the week I was going to get a full game," Wallis said.
"I was going to get my mind set on that. Collingwood have been so dominant in the last couple of years so it was going to be a big task. They were able to step up to the plate tonight."
Most AFL players are yet to know the frustration of starting the game with the green vest and Wallis admits it does cause a vastly different approach to the game.
"In terms of being a sub you do (prepare differently). But if you start on the bench you're on within the first couple of minutes so it doesn't really affect much. It was a good thing to start on the ground on the MCG against Collingwood. It was a dream come true," he said.
The Bulldogs drifted in and out of the game but the 18-year-old put in a consistent performance, gathering 16 disposals and using his body well against the hardened senior Magpies.
"I spoke with Monty (forwards coach Brent Montgomery) and one of my roles was to use my body and try to keep the ball inside, tackle and harass. That was my role so I tried focusing on that," he said.
"I love the contested game and that is the style I want to play and the style I want to build on in the next few years to play that way."
Wallis said he had been gaining advice from close friend and teammate Tom Liberatore who has played in all five of the Bulldogs matches so far.
"He said your phone goes crazy in the lead-up because everyone knows you're going to play your first game. He told me you've got to keep it basic, turn your phone off and concentrate on your footy," he said.
"In the first five minutes you've got to get your body on and just play footy. It's big stakes but it's just another game of footy. He's done really well in his first few games."
