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.
