Ryan Mason accepted his side just weren’t able to get through the first ten minutes of Saturday’s encounter with Coventry City directly after they were reduced to ten men.
The Baggies were leading 2-1 in the opening period of the second half at the CBS Arena thanks to Aune Heggebø’s brace, but Jayson Molumby picked up a second booking for a foul on the halfway line.
The hosts, who sit top of the second tier, went on to score two quick goals with Ellis Sims and Victor Torp on target.
Mason insists it’s an experience his group have to learn from and avoid in the future.
The boss said: “It’s frustrating. We gave them the opportunity to get back into the game, and that’s the most disappointing thing.
“We started the game really well. I thought we played some really good football in the first half and we showed lots of personality and quality. We also scored two really good goals, but we were really disappointed to concede at the end of the half.
“The game completely changed in the second half from an incident. It’s something we need to learn from and avoid in the future because to play with ten men in this league against quality opposition, it’s going to be extremely difficult.
“We weren’t able to get through that period straight after the red. We didn’t find a way to get through and they scored a couple of goals from set-pieces and second-phase set-pieces, which we need to better on.
“It was a difficult and a frustrating second half.
“I had so much belief and confidence in the group. I think we started the second half well and we had a lot of control and I could feel that we were going to cause them problems. We certainly did that in the first half and I was sure we were going to do it in the second too.
“We have to learn from this and grow from this. We have to accept why this has happened today and make sure it doesn’t happen again.
“It was a challenge for us to halt the flow of attacks. There were different phases after the red. The crowd were up as soon as the sending off happened and they sensed the importance of that ten or 15-minute period. We conceded two goals in that period and that was tough to take.
“You then go into a ten or 15-minute period where you don’t want the game to get away from you and you don’t want that to happen. I thought we handled that quite well.
“We then had ten minutes at the end where we could open up a bit and take some risks, but sadly nothing really materialised.
“We had a couple of situations where we could’ve made something count, but we didn’t. It’s difficult to play for that period of time with ten. It’s tough.”
