The Brazilian accepts Chelsea are facing "the most important game in the group" in their bid to reach the knockout stages of Europe's premier club competition, and that there is no time to dwell on their Hawthorns setback - the fourth Premier League game in a row which the Blues have not won.
"The dressing-room reaction after the game was that we were upset and angry," Luiz said.
"We were disappointed because we should have won the game. There were raised voices but that is normal. This is a big club and we don't like to lose games. We missed the moment but all we can do now is look ahead to the next game.
"What's past is past and the future is Juventus. It will be difficult and Juventus are a great team. They are just one point behind us. This is the most important game in the group."
Luiz is aware Chelsea have to get the balance right between challenging for the Premier League title and striving to retain the Champions League.
He said: "It's not good at the moment as we started the season at the top of the league, but all the big teams have come to West Brom and it's not been easy for them.
"West Brom have a good philosophy and a great coach (Steve Clarke) but we are disappointed, because Chelsea want to be top of the table always.
"In the Champions League we have a great opportunity to qualify even though Juventus and Shakhtar (Donetsk) are both great teams.
"But we will never forget how important the Premier League is. There is a bit of a gap at the top and we don't want to get too far behind the other teams. In two or three games everything can change and Chelsea will be fighting for the top of the league again."