Joelinton struck for the 1-0 win, with Fabian Schar also being sent off for hosts Newcastle.
The Brazil midfielder later said: “Southampton are a very good team. They made it difficult for us but I think we did well in the end. The team showed great character to defend and it’s great to start the season with a clean sheet.
“We need to take things game by game. This is just the start. We have big goals this season but we have to make sure we’re ready for when the games come along.
“Last season was very difficult for me with injuries. I had a great holiday and I’ve come back fresh. I worked hard in pre-season and I’m ready. I’m very happy to get the goal and help the team get three points.
“I love to score goals and want to score more goals this season, but the most important thing is to help the team, whether it’s with goals, assists or runs back.”
On Schar’s sending off, he added: “I need to see it again, but we’re happy in the end. The team showed great character to fight for each other.”