Southampton allowed Philippe Coutinho to score a scrappy goal in first-half stoppage time that set up a nervy second 45 minutes - and the team got an earful from their boss.
Pochettino said: "We are an attack-minded team and always want to push forward so it's not such a big deal if we concede a goal when we are pressing really high to get a goal for ourselves as well.
"But to concede when there are 10 of my players in my own area, in my own box, and concede a goal like that I can never tolerate that. I was really angry when I went into the dressing room at half-time. It changed what I said to my players. That is my job."