Tottenham had not been beaten in the league since their opening match at Manchester United in August and a win would have seen them go above Louis van Gaal's side into fourth place.
He said: "One nil up always gives the opponents the chance to come back into the game.
"We lost concentration and made easy mistakes, we started to give the opponents the belief they can win the game.
"The chances that we conceded were easy for Newcastle, we need to analyse the game.
"Our first half was fantastic and our second half we need to analyse - I want to see the game again."
The Argentinian is not worried about his team's ability despite the result, and believes they still have what it takes after boos were heard echoing around White Hart Lane at the final whistle.
He added: "(Am I) concerned? No. In football you can always improve.
"After the first half we were happy in the stadium but in the second half it was not the same, it was a bad night for us."