The Saddlers went into half-time with a one goal lead from a Stuart Sinclair goal but capitulated in the second half, conceding three.
A poor mistake from Danny Guthrie gifted the hosts their second goal and Clarke was left disappointed with the result.
“Not good enough is it, the second half performance,” he said.
“The biggest disappointment for me, we’ve given a sloppy second goal, their left-back has scored a great goal with his right foot, they haven’t really created many opportunities and got us on the counter a little bit.
“But, the biggest thing for me is when you’re in control of a game to really be clinical and finish your chances and we haven’t done that today.
“We haven’t committed the good final ball, we worked opportunities to be ruthless and clinical and we didn’t do that.
“Obviously the goals we conceded, which is unlike us.
“The last two games you concede six goals in two games and you’re not going to win football matches.
“Three or four of those goals have been individual mistakes.
“Every goal you can look at two or three things in the build up but we’ve handed them on a plate, so it’s been frustrating, very frustrating second half.”