Having led against Tottenham Hotspur, Saints ended up on the wrong end of a 3-2 scoreline as the North Londoners left St Mary’s with all three points.
And Pochettino was left angered as the team squandered an early advantage to slip to defeat in what is Southampton’s sixth game without victory.
“I think – in the second half in particular – we got dressed up as Santa Claus and gifted them with many chances,” bemoaned the manager.
“Over the 90 minutes there were different phases to the game, there were some positive aspects and some not-so-positive aspects.
“In the first half there were chances for both teams. When it was 1-0 we had the game under control - we could have even scored again to make it 2-0, but then we conceded the goal and practically gifted them the 1-1.
“We made a lot of mistakes and in the Premier League if you make mistakes like that then you will get punished.”
Adam Lallana’s opener had been cancelled out by Emmanuel Adebayor to level things up at the break, at which point Saints looked the more likely side to score again.
But, even after Rickie Lambert levelled matters following Jos Hooiveld’s own goal, Pochettino felt Saints always had an uphill task on their hands having fallen behind for the first time.
“At the beginning of the second half we were controlling the game, but then after we conceded the second goal it was really hard to get back into the game,” he said.
“We were risking a lot in order to try and get level with them, and then they caught us on the counter attack and we just couldn’t get back at them.
“We have to keep on working and believing as a team,” added Pochettino, who now leads the team into away games against Cardiff and Everton over the Christmas period.
“In the past we had a run of seven games winning when we were looking up, but now it is the opposite. We need to keep working.”