Mane set his side on the way to their 2-1 victory at St Mary's when he fired them ahead just before the half-time interval.
And the Senegal international was quick to pay tribute to his former club afterwards.
"I'm sorry it is against my old team and sorry I have to score but I'm wearing an LFC shirt now," Mane said post-match.
"Southampton was a very good step for me, I have big respect for this club. It's an amazing place.
"But it's part of football and you have to deal with it."