The Baggies were 4-0 down in their third round tie with just 30 minutes on the clock at The Hawthorns and Mowbray slammed his side's lethargic start.
"The game was lost in that first 30 minutes," he admitted after the match. "But the bigger picture gives me some food for thought on one or two players.
"It's a learning curve for me about my squad and my team, the ones you can trust and the ones you can't. The first half-an-hour was a bit too much for some of them.
"One or two will find it more difficult to get run-outs now and there have been a few lessons learnt by us all. It was a bridge too far for us.
"I'm now looking for a response from the team on Sunday when we play Queens Park Rangers and we'll be trying to put things right at the weekend."