The 20-year-old, a former Scotland age-grade captain, was thrown straight into a tough test against All Blacks star Reiko Ioane but rose to the challenge impressively.
"I was so keen to tell him [he was starting]," admitted Smith when speaking to Premier Sports. "But I don't like to go back on my word so I made sure he settled in nicely on Monday.
"He stepped up and did a very good job tonight for us, and put his hand up for more responsibility with us.
"With Kerr Yule and Kerr Johnston, the age group of that centre group has now dropped quite a bit. When the young guys play amongst a little more experienced players, they get an opportunity to be themselves.
"We did it with Seb Stephen last year. He played Leinster after we lost against them in the quarter-finals [of the Champions Cup]. He stepped up. Maccenzie Duncan's first game was then, too. Sometimes the occasion demands it and when the players step up, it's fantastic."
Despite Glasgow's strong record at Scotstoun, the scale and style of their win over a stacked Leinster side still raised eyebrows.
"The boys worked hard," Smith said. "We were going to try and score as many tries as possible, but I didn't think we'd get to that many. Some good attack from our side, managing to hold the ball.
"I'm really glad we made full use of the cards they have. I'm not oblivious of that fact, but still I thought we played really well.
"It's the way we train, the way we try and develop the game. The game is going that way. If you look at the Six Nations now, there's a lot of tries scored. It's what's demanded of the game now.
"That is the one ingredient that brings the enthusiasm to club rugby. I'm really proud of the boys."