Lambert's men have failed to score in their past five matches in the Premier League - losing all of them - with their most recent goal coming in a 1-0 win over Liverpool at Anfield.
The drought extended to 531 minutes at Loftus Road, but Lambert slammed his defence for allowing Charlie Austin to penetrate their defence in each half.
"I thought the two goals we lost were really poor," Lambert said.
"I think that's the most we've had the ball, possession wise but that's why I've never gone really far.
"The main stat is putting the ball in the net, and keeping it out. I thought we defended poorly for the two goals.
"I think we've got to be more clinical in the last third. The two goals are disappointing because we had most of the ball."
Lambert said he felt Villa were on top when they conceded on both occasions.
"I knew it was always going to be a tough game, but I was pretty pleased with the way we held the ball and what we were doing with it," the former Norwich City boss said.
"We just had to be more clinical in that last third of the pitch. The two goals we lost were shocking, especially when we were on top.
"My main concern tonight was you have that much of the ball, you've got to score with it. But also you've got to defend when you're on top."
Christian Benteke was making his second league appearance back from an Achilles injury, but Lambert said he would remain patient with the Belgian striker.
"The injury he had was really severe, that was only his second game in six months," Lambert said.
"It's a long time he's been out. He may have to wait six, seven games until he gets up to speed. There's little things he's getting [better] at."
Lambert refused to single out any of his players, and when asked if Irish midfielder Jack Grealish would be handed an opportunity at Premier League level, he responded: "I'll rely on everybody, not just on one lad. He's not started a Premiership game. As a team, we have to regroup."
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