The striker's 85th minute saw Saints earn a first Premier League win for the season.
“It means a lot,” Armstrong began. “I think you've seen the last few results haven't gone our way, but I feel like we’ve been playing well, as daft as that sounds. What a shift from the boys today - a bit of luck on our side as well. And yeah, what a three points.
“We all worked hard all week because we knew it was a big game, there’s no beating around the bush. They're a good side, and we knew it was going to be tough and they were going to make it hard for us, but the lads dug in and I thought the lads were excellent and it shows on the pitch when you win.
“I thought the lads at the back were excellent today. They beat up their strikers and got us going. The way they play out from the back is incredible and the gaffer's telling them to do that, the lads are all buying into it, and look, I know it's going to be tough in the Premier League, but if everyone gets behind us you can see what we can make it at St Mary’s and yeah, unreal.
"When you’re constantly attacking it gives the crowd a lift. That's what they want to see, attacking play. And yeah, I'm just over the moon to get that goal and get the three points."