Danny Welbeck admitted to harbouring mixed emotions after United's 3-3 draw with FC Basel on Tuesday night.
The young striker, in his first start since picking up a hamstring injury against Arsenal in late August, scored twice to fire the Reds into an early 2-0 lead. But the Swiss visitors rallied to first equalise and then go ahead, before Ashley Young snatched a draw with a late header.
"To get two goals in the Champions League, I'm over the moon with that," Welbeck told Sky Sports. "But it's a team game and I'm disappointed.
"We went into half-time 2-0 up and Manchester United should be finishing teams off. It's just not like us [to let teams back into games].
"In the second half we didn't start as bright as we should have. They gradually worked their way into the game and pulled two goals back quickly."
Welbeck praised Basel's approach to the game and says the Reds struggled to deal with their patient, passing football.
"As good teams do, they came out and passed the ball well," he said. "They played it from the back well and we found it difficult.
"We're really disappointed with the result today. But we just have to get back into training and get on with it."
United's next outing comes on Saturday 1 October at 3pm, when Sir Alex's men welcome Norwich City to Old Trafford in the Barclays Premier League.