Garner, 19, opened the scoring in the first-half as his first-time shot from the edge of the box somehow found a way into the net after a goalkeeper error from David Marshall.
"The goal was a good feeling, that is my first professional goal," he told club media after the match. "I have had a lot of chances this season and the ball just hasn't gone in the back of the net. So for it to go in, it was quite fortunate as I didn't hit the ball as sweet as I could have but I am made up.
"I know that if I can get the ball out of my feet on the edge of the box, I can score goals. I have done it growing up through the academy so when I do get the chance to have a go from the edge of the box, it doesn't faze me and it is something that I need to keep on adding to my game."