The Senegalese spent two years in Salzburg before leaving for Southampton in 2014.
Speaking after the 2-1 win to BT Sport, Mane said: "It was a really tough game. We created many chances.
"I'm happy for Naby. We deserved to win. We are happy."
On playing against his old club, Mane said: "It's always nice to come back here because this is where everything started for me.
"I'm really grateful to the club and fans. Sorry guys but we have to do it."