Clarke had seen his side fall behind to Gary Hooper's 13th-minute opener, before a second half in which the hosts dominated ended with Leroy Fer's goal on the break a minute from time.
West Brom spurned a number of opportunities during the second period, going closest a minute after the restart when Stephane Sessegnon saw his effort blocked at close quarters by what appeared to be the arm of Martin Olsson.
Sessegnon missed an even more presentable chance five minutes later, but Clarke felt that should have been irrelevant.
"The first chance he missed at the start of the second half was going in the net," Clarke said. "It hit Martin Olsson on the arm, which stopped the ball going into the net.
"Whether the referee saw it or not doesn't help us. And I'm not sitting here crying about a penalty decision because it's a tough one to call.
"But the ball was going into the net so it's hard to say that was a big miss."
On a more positive note, Clarke heaped praise on Uruguayan defender Diego Lugano, who made his first Premier League start in place of the suspended Jonas Olsson.
"I thought he did well; I was pleased," Clarke added. "It's difficult for him because he hasn't had too many starts for us.
"I thought he acquitted himself well in the second half when we risked a lot and he was exposed to the counter-attack. I thought all the defenders stood up to be counted."
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