The Brazilian had been criticized after seemingly exaggerating the impact of the challenge from his countryman, but the Chelsea boss feels that the real issues are being ignored.
Red Devils fullback Rafael was sent off for a kick on his fellow Brazilian and the Blues man was caught on camera seemingly laughing while on the floor, apparently in pain from the challenge.
Benitez insists that his player's smiles were due to abuse from fans rather than any nefarious intent, insisting that more important issues were being overlooked to discuss his facial expressions and praising the defender.
"I'm aware that David Luiz is one of the best players in the Premier League, by miles," he told reporters. "Miles away of a lot of players, so he is one of the best, without doubt. I think that, talking about [Rafael's sending off], we are not talking about Chelsea beating United, doing much better than United in three games.
"David Luiz was laughing because the fans were abusing him and after was the red card, so it was very clear, the timing, but we continue talking about this instead of trying to eradicate the bad tackles that you can see every week. I think we are giving importance to something that is not as important as the other things."