Manchester United boss Erik ten Hag was pleased with their 2-1 win at Luton on Sunday.
Rasmus Hojlund struck twice for the visitors, with Carlton Morris pulling a goal back in the first-half.
Ten Hag said: "It was very good but then we had big chances to score more. We dropped too deep and allowed them to get back in the game. We didn't close the half spaces. It got difficult. We had big chances in the second half and we didn't take them.
"We should have scored in the second half with Bruno, Garnacho and Rashford. One has to go in and then you make your life easy. We kept them in the game.
"We are dropping too deep and we lost a bit of focus maybe because it was so easy in the first 10 minutes. We can't afford this especially against a side like Luton. They have really upped their trend in the last few weeks."
On Hojlund, he also said: "We recruited him on his character, I knew it was strong. He can really perform under stress and that is something you need a Man United striker. He doesn't get nervous or lose confidence. He has a lot of confidence and I'm sure he will score even more.