It was the defender's first goal for the season.
"I’ve missed a few chances this season, so it felt really good to get a goal," Colwill said afterwards.
"Of course, it was against a team I played for when I was young, and it’s the city I live in. I have a few friends who are Southampton fans, so it meant a lot to me. I grew up around St Mary’s Stadium, that’s where I learned a lot of my traits, so it meant a lot to me."
Colwill also stated: "The last few games have been tough, so it was important to bounce back.
"To get those goals, keep a clean sheet, and most importantly boost our confidence – hopefully, we can take it on to the next game.
"We all trust each other and knew it would come. Every team goes through bad times or tough patches, we just have to get out of it and that’s what we did today. It raises our confidence."
Fellow academy graduates Tyrique George, Josh Acheampong, and Shumaira Mheuka all featured on the night.
Colwill also said: "It’s amazing for the boys to come on. As an academy boy myself, I know how much it means to them.
"They were amazing when they came on – Tyrique got the assist, Shim was amazing, and Josh came on and was solid. I’m so happy for the boys, and hopefully, it continues and they keep progressing in the right way."