The England international striker was introduced 11 minutes after the half-time break on Saturday and scored just over 60 seconds later to double the hosts' advantage.
Lambert also laid on Southampton's third for Jay Rodriguez as Pochettino's side climbed above Newcastle United and back into eighth place in the Premier League thanks to the victory.
Pochettino felt opting not to play Lambert from the start was beneficial for both the player and the team.
"As a manager I am always looking for what is best for the team and (for) every player and I thought Rickie coming on as a sub would be good for him and it was," he said.
"Sometimes tactical decisions go your way and that was the case.
"Our philosophy is always similar. We made some changes to variables to favour our attacking intent (and) I think Gaston (Ramirez) and Adam (Lallana) linked well.
"We were just looking through fresh alternatives, which we can use for the rest of a long season."
Pochettino also confirmed that a Norwich player stepped on defender Dejan Lovren's testicles during the game, explaining: "One is inflamed and swollen."
