Mauricio Pochettino has called for Tottenham to show the consistency needed to challenge for the Premier League title.
Spurs made it three wins from three matches in the Premier League with a 3-0 victory over United at Old Trafford on Monday.
All the goals came in the second half after United had failed to take several chances they created before the break.
And Spurs boss Pochettino told Soccer AM's Tubes: "Our performance wasn't great like the perception was, that's why it's important to assess, and our responsibility as coaches is to show the players and to see the reality.
"After 3-0 at Old Trafford it's easy to praise everyone but the most important thing is to be clever and assess the game and see what is going on with the team. It's so important to be consistent and we need to improve a lot of things to be a real contender.
"A dream is a dream but it's important to be realistic and improve to be a real contender. It's only three games, of course it's important to win, but we need to be consistent."
Pochettino said after the match that it was a "massive victory" as Spurs started a top-flight season with three wins from three games for only the fifth time in their history.
However, having had time to assess the display, he said: "In the first half it could have been 2-0 or 3-1 to Manchester United and we conceded a lot of chances and our performance wasn't great.
"It's still so early to talk about winning titles. Now is the time to build performances, build individual players and the collective, be solid, and if we can be solid and consistent then at the end of the season maybe we can talk about winning, but it's so far away today."
Tottenham will be looking for a fourth straight win when they go to Watford on Sunday, live on Sky Sports.