The loss underlined Chelsea's troubles away from Stamford Bridge, with their five games on the road this term yielding only five points.
|3/10||Chelsea are 3/10 with BetVictor to beat West Brom in their next Premier League clash on Saturday|
The Portuguese manager was particularly riled by the performance at St James' Park, where second-half strikes from Yoan Gouffran and Loic Remy put the visitors to the sword.
"At home, five games, five victories and away, five matches, one victory, two defeats," Mourinho told the club's official website.
"We can also say that we played away in very difficult stadiums. We played at Man [Manchester] United, Tottenham, Newcastle and Everton, we played in probably the most difficult places to go.
"But I have to analyse it by another perspective which is the perspective of why we don't do better and why especially on Saturday because that was the worst.
"Against Everton [Chelsea lost 1-0[ we were really unlucky because we had a fantastic first half and in the second half we had a clear penalty for us and the referee didn't give it.
"At Newcastle we had the kind of match we have to analyse deeply because it was the worst."
The defeat ended a run of six consecutive victories in all competitions for the London club but Mourinho dismissed the notion that complacency had got the better of his side.
"You have to know why you win and you don't win by a miracle," he added. "You win by effort, you win by commitment, you win by ambition, you win by quality and you win by expressing yourself individually but in the team context.
"You have to know why you win and I tell my players every time I can, every time I have meetings with them, 'don't forget why you are getting results'."