The Welshman, playing against his former club, scored the decisive goal in the second half, but admitted that his team were not at their best at White Hart Lane.
"It is a massive three points and keeps our Champions League hopes alive," Bale told BBC Sport.
"Southampton played very well. The first half we didn't play well, the second half we were more confident and we got that decisive goal."
Spurs are now level on points with fourth-placed Chelsea, but have played a game more.