Jose Mourinho accused his Manchester United players of failing to listen to his warnings about Tottenham's kickoffs after watching his team concede a goal after just 11 seconds at Wembley.
Christian Eriksen put Tottenham 1-0 up with his first touch before a Phil Jones own goal made it 2-0 after 28 minutes.
Mourinho revealed afterwards his players had watched videos of the way Mauricio Pochettino's side start games but admitted the planning had not paid off.
He told BT Sport: "We made a bad mistake for the first goal. It was a global by the whole team because they watch videos and they analyse Spurs' kick-off. They know the way they do it.
"We lose the first ball in the air, we lose the second ball on the ground and then we lose the cover inside when Eriksen makes the run. It's really, really, really a bad goal.
"The second goal mentally killed us and gives Tottenham the chance to play the way they like to play. At 2-0, the game is in their hands.
Mourinho, who handed Alexis Sanchez a Premier League debut, tried to get United back into the game in the second-half replacing Paul Pogba, who was not injured, and Jesse Lingard with Marouane Fellaini and Juan Mata after 63 minutes.
However, Fellaini only lasted seven minutes before he was replaced with Ander Herrera after he picked up a groin injury.
Mourinho added: "I think I was unlucky with Fellaini because I want to change the structure and dynamic of the team and after a couple of minutes he's injured.
"It's always the same thing. It's not a big, big thing but we felt something and he was telling us he could not carry on."