Television pundit Ian Wright had labelled Luiz a "coward" for the challenge, which came with Chelsea already four goals up.
Benitez said: "I see hundreds of tackles in the league that are more dangerous than that one. I won't say it wasn't bad - it wasn't the best - but a factor was the size of the other player.
"David Luiz is a great player and we have to be pleased he's playing in the Premier League. It was bad luck."