Mellberg's throw-in was missed by Finnish keeper Enckelman, and the ball rolled into an empty net, with referee David Elleray feeling the Villa number one had touched it with the bottom of his studs.
"You can't believe that it is true," complained Swedish international Mellberg.
"I threw it towards Peter Enckelman to allow him to start an attack. But I feel that Enckelman never touched the ball."
The centre back was not best pleased with Elleray's refereeing throughout a typically brusque Birmingham derby.
"It's typical," he told Expressen. "But the performance of the referee was the worst for a long time.
"It wasn't our match."
A dejected Enckelman, who was cruelly taunted by a Blues fan who invaded the pitch to celebrate the goal, did not feel he had touched the ball on its way into the net.
The Finn did not appeal against the decision, and Villa boss Graham Taylor suggested the Scandinavian was unaware that the goal should not have counted if the throw-in crossed the line directly.
"I don't know if I touched the ball," he grumbled. "I don't think so.
"If I did, it must have been a minimal touch."