At one stage, it looked as if Chelsea would be out of the FA Cup having trailed 2-0 at Old Trafford before mounting a stirring comeback which on another day could have seen them go on to win the tie.
Luiz accepts it was perhaps a missed opportunity.
He said: "People saw the match and in the second half Chelsea controlled all the game and we had the opportunities to win. I felt a little bit sad, but now we have another game to win.
"We have an opportunity on Monday. When you do well on the pitch (against them) this gives you a lot of confidence."