Mane concedes that a big opportunity has gone begging for his side, but is still hopeful of getting the job done against Colombia.
"Frankly, we're a bit disappointed, and that's normal because there was a way for us to win this match," he is quoted as saying by FIFA's official website. "I felt we started the game well but then we let them back into it.
"But we can't underestimate the Japanese team - they created quite a lot of opportunities and scored twice. Now we have a decisive match next week and we are going to prepare really well in order to qualify - that's the only thing left for us to do."
Senegal and Japan have four points apiece from their opening two group matches, while Colombia and Poland - yet to get off the mark - face off in Kazan on Sunday night.