Watford scored a brace in each half to comprehensively beat Blues, although they did fashion a number of chances themselves at the other end without finding the back of the net.
“We played against a very good team with some very good players,” said Clark. “They were technically very good and probably some of the best in the division.
“I think the difference between the two teams was in both final thirds really. They had some good movement and scored some good goals.
“We made bad decisions in terms of individual defenders who enabled those goals to happen and that was the difference.
“There was nothing in the game in the first 35 minutes and in the middle part of the pitch we’ve done quite well but as I said the two final thirds where it matters has been the difference.”
Without singling out individual players, Clark felt some of his side’s defending could have been much better.
“On our behalf I think all four goals can be put down to poor decisions and poor bits of play,” he said. “And when they've got the ability they have they’ll do what they did to us.
“We win together and lose together and we don’t single out different parts of the team, we do it as a group and we make sure we bounce back.”
Clark now has just three days to get his side back into the groove when they welcome Sheffield Wednesday to St. Andrew’s on Tuesday evening and he is determined to lift them ahead of that test.
“We've got to dust ourselves down and be men about it and get our chins up and chests out and be ready for a very tough game on Tuesday evening,” he added.
“We’re hoping that Marlon (King) will be back for Tuesday and also that one or two others will be available as well.”