Marlon King's own goal decided a drab derby, and afterwards Clark expressed irritation that his side had failed to take advantage of results elsewhere and climb the Championship table.
"Today's results (elsewhere) gave us an opportunity, the top six hadn't moved any further away from us before kick-off. We could have actually moved closer to them," Clark said.
"I made a point of saying that to the players, a win would have taken us six points off.
"I spoke pre-match about chipping away at those nine points and the teams ahead of us and trying to cut that gap come January.
"Unfortunately we've just stood still, really. I'm disappointed with that and it's forced hand in hand with the inconsistency at the moment."