The Baggies surrendered a 2-0 lead to lose 3-2.
Clarke looked shellshocked after the game and he was at a loss for words to describe how the Baggies threw away such a dominant position.
"We had good control and I certainly couldn't see the finish to the game that happened," said Clark, who denied it was down to complacency or a sense that his players felt the game was won.
"I am disappointed. I am not sure (what happened). I can't be more honest than that.
"We should have scored four or five but then we lost a goal and for some reason we lost our shape and we lost our composure and conceded the two late goals that cost us the game.
"When you contrive to pull a defeat from what should be a comfortable victory then it is something we will have to look at.
"Football can be a strange game and today is one of those days."