Eriksen nearly set a record of his own with his stunningly early goal, scored after 11 seconds, just two seconds slower than Ledley King's goal against Bradford.
"After 10 seconds, we made a ridiculous mistake", Mourinho told reporters.
"The second goal mentally killed us and gives Tottenham the chance to play the way they like to play".
And Jose Mourinho was furious with the result and labelled both goals "ridiculous".
The £20million January signing became the first Toffees player to score twice in his maiden Premier League appearance at Goodison Park since Romelu Lukaku against Newcastle in September 2013 with a first-half double.
"We lose the first ball, the second ball on the ground and the cover inside for Eriksen, so a really, really, really bad goal".
"After the first goal the team had a good reaction - we were there and tried to create".
Antonio Conte suffered one of his worst Premier League defeats at Chelsea after three second-half goals in the space of 16 minutes from Callum Wilson, Junior Stanislas and Nathan Ake earned Eddie Howe his best top-flight win with the Cherries.
"He came off because he had something in his knee", claimed the United boss. "He came on with enthusiasm, but he has an injury in his ligament".
Christian Eriksen's goal was his 50th for Tottenham.
But Mourinho said conceding an own goal had done nearly as much damage to the visitors' morale as Eriksen's extraordinary opener. "I don't think it's a big thing but he was telling us he couldn't carry on". "We're sure he's going to help us", Pochettino told the BBC.
The strike put Spurs into an early lead in their eagerly-anticipated clash in front of a massive Wembley crowd of 81,978 - a new Premier League attendance record.
For the first time United seemed to have remembered they were supposed to be the second-best team in the league but then, just as quickly, Spurs regained the initiative and "olés" could be heard as the home side embarked on another period of superiority.