United have now gone four games without a win in all competitions.
Mourinho has come under increasing pressure in recent weeks because of those results, and was involved in an apparent training-ground dispute with midfielder Paul Pogba last week.
“The players tried. They raised the level of their efforts,” Mourinho said.
“They raised the level of their intensity.
“We tried to play but in some crucial positions in the building up phase, we don’t have the technical quality to build from the back.”
United have not won at home since 10 August – the opening day of the season. They lost 3-1 to West Ham in the Premier League on Saturday, three days after they went out of the Carabao Cup to Championship side Derby.
Mourinho reacts to Scholes and boos
Former United midfielder Paul Scholes said before Tuesday’s game at Old Trafford that he was “surprised” Mourinho was not sacked after Saturday’s defeat at London Stadium, as “the performance was that bad”.
Scholes, who made 717 appearances for the Red Devils, also told BT Sport that Mourinho’s “mouth is out of control” because of the way the Portuguese criticises his players and the club.
He added the former Chelsea and Real Madrid manager is “embarrassing” United.
Mourinho said he was “not interested” in Scholes’ comments.
“Freedom of speech. Free country. You can say what you want,” he added.
Mourinho also responded to the Old Trafford crowd’s chants of “attack, attack, attack” during the game, and the boos which came at the final whistle.
“It’s freedom of speech, especially for Manchester United fans who I respect 100%,” he said.