Ashley Westwood broke the deadlock with a wonderful free-kick as Villa made a strong start, but Wayne Rooney quickly equalised and then fired United ahead from the penalty spot on the stroke of half-time.
Juan Mata made it 3-1 and Javier Hernandez notched a late fourth, but Lambert felt the margin of victory flattered United and was still able to take a lot of positives from his side's display.
Lambert also refused to criticise Christian Benteke, despite the Belgian striker missing a couple of good chances in the second half.
"I didn't think there was much in that. The scoreline was pretty harsh on us," said Lambert on the club's official website.
"We started the game great, looked really good, had plenty of the ball and looked very threatening, then Westy scores a terrific free-kick.
"We lost a poor goal with the header but Wayne Rooney can do that.
"The second goal was a penalty - a clear penalty. Then we came out in the second half and Christian has a really good chance.
"I won't be critical of him, though, because he's scored vital goals for us.
"But overall, we were definitely a handful. I always felt we could get something out of the game.
"But when you come to places like this, you have to take your chances when you get them.
"I thought the scoreline was pretty harsh on us. We had chances to pull it back.
"You're obviously disappointed about being beaten 4-1 but there's a lot to take out of the game."
The result left Villa in mid-table on 34 points, and Lambert is confident they can enjoy a good finish to the season.
He added: "You keep going for the team above you.
"We're in a decent position but we need to get another couple of wins or so.
"I don't set a points target because if you do and you don't hit it, it becomes disappointing."