After opening the scoring in the 12th minute, Pochettino's side conceded three goals in the last 10 minutes as they let in seven goals for the first time ever on home soil.
With questions quickly being asked of the Argentine post-match, the Tottenham coach conceded his team lost their fighting spirit in the closing stages of the contest.
“The feeling at the end, when we conceded the three goals, it was like the team was tired and gave up a little bit,” Pochettino said.
“Maybe that showed a little bit our frustration in the game because up until 83 minutes the team were alive, we were fighting, trying to create chances to score a third goal and we were still in the game. But they were very clinical.
“Of course we are so disappointed. I cannot say another thing other than I feel very very disappointed. I feel so bad because when you concede seven goals it is tough, but you need to face up to this type of situation.
“When you play the final of the Champions League, it was nice to put your face up after the wins we had at Manchester City and Ajax. Now I have to put my same face up and accept we were not as good as we expected.”
Spurs have won just one of their last five matches in all competitions and were knocked out of the Carabao Cup last week by League Two side Colchester.
Having reached impressive heights last season, Pochettino believes this campaign will be a difficult one for the club as it looks to refocus.
“This is going to be a tough season,” he said.
“After the final of the Champions League, it was a chapter closed and now the club is in a period when they need to open another chapter and decide a project, medium, long-term.
“You need to show your quality like a man first, to face the situation like a man. You need to use your quality, how you are strong, to face this type of situation. What comes after is the professional side. Now we need to be a man and be strong all together to try to bounce back and change that feeling.
“I think it’s more psychological now. To try to move on and make sure there is no damage between us and talking in different ways to each other.
“The most important thing now is to have one idea, one analysis, one assessment. We need to stick with this assessment and, from there, start to improve.”