Spurs boss Mauricio Pochettino has told his side they will "crash" if they start to believe they are the real deal after their impressive win at Manchester United.
Spurs put out a real statement of intent with a 3-0 victory against United on Monday, with many now believing they can challenge for the Premier League title.
But Pochettino was not happy with the first-half display at Old Trafford and has told his players to believe the "reality" rather than "perception".
Spurs are at Watford tomorrow and the Argentinian has warned against any complacency. He said: "My mood wasn't great. I was so disappointed. I think we need to improve our performance.
"The first half I wasn't happy and I translated that to the players. We need to fight against the perception. When you compare the perception and the reality, we need to talk about the reality, and the reality was in the first half we can concede one, two or three goals.
"But of course the team showed character and in the second half we were much better. But if we want to fight for big things, we need to show we are contenders for 10 months.
"We're playing against a very good Watford team - a team that's in a very good moment.
"After three games they're over the moon. If we're not ready and believe because we beat United 3-0 that all is fantastic, I think we are going to crash.''
Spurs were handed a tough Champions League group draw against PSV, Inter Milan and Barcelona, where Pochettino owns a house.
He added: "I'm going back to my town Barcelona. It's always exciting to play against sides like Barcelona, Inter Milan or PSV, who are a young team."
Spurs are without goalkeeper Hugo Lloris at Vicarage Road after he picked up a thigh injury.