The 21-year-old was promoted after ruckman Mitch King was placed on the long-term injury list.
“It’s a bit of a shock and I didn’t expect it,” Smith told Melbourne TV.
“A year ago, I was playing in the VFL Development [League] and here I am now playing round one against St Kilda and I’m rapt.
“All of the hard work has paid off and I just can’t wait to be out there.
“As pre-season went on, I was training really well and I thought I could actually do this.
“I played a couple of JLT [Community Series] matches and the last few weeks I’ve been thinking about it and it’s been in the back of my mind.
“Now I’m playing, I’m ready to go and I can’t wait.”