But the centre-back and his team-mates will have little time to reflect on the setback, which has left them four points adrift of leaders and champions Manchester City.
Luiz accepts Chelsea are facing "the most important game in the group" in their bid to reach the next phase of the Champions League when they visit Juventus on Tuesday.
"The dressing-room reaction after the game was that we were upset and angry," the 25-year-old 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."
Luiz refuses to accept that Chelsea need time to gel in the same way as Shakhtar have reaped the benefit from building their side over several years.
He said: "This is the big season. We need to live in the present.
"When you work under one guy for a long time, yes, you know more so all the players know we have to be stronger on the pitch."
Chelsea boss Roberto Di Matteo knows his team have to improve defensively after conceding 18 goals in eight games.
He also reiterated the possibility of changing the formation and personnel if it will make Chelsea a more solid unit.
The Italian said: "I think as a team we have to be better defending. You don't defend with one player - you defend with the whole team, like you want your whole team helping when you are attacking as well.
"It is a defensive organisation on the pitch that we need to look at and, as I said before, maybe I have to do some changes.
"We have got bodies in midfield - the 4-2-3-1 system really helped us last season after the change (of manager) but maybe in terms of personnel we have to do something different."
Di Matteo conceded Fernando Torres was one of the players who could lose his place after an ineffective display at The Hawthorns.
He said: "Am I prepared to leave Torres out on Tuesday? I think we will have to assess the whole team and see how everybody is, and how they have recovered.
"A lot of players only came back Thursday afternoon or Friday from internationals in Europe and the rest of the world.
"We will assess them and see what the right selection is for Tuesday. If I believe it is the right thing to do for the team, then yes."
Di Matteo is also at a loss to explain another dip by Chelsea during November.
He said: "It is very difficult to explain. It is not just one year - it has been three years in a row.
"You have top, top players - they play every three or four days. That amount of games can affect them, but it is not only that.
"It is a challenging time when you don't win games and you need to instil confidence in players and to the team and that is going to be a tough job."