Sam Williams struck from the penalty spot in injury time to claim victory for the home side after Youl Mawene was adjudged to have fouled him in the box.
But Mellon was not pleased with the decision. He said: "I think there's not a person in the stadium who thought it was a penalty kick.
"I don't know how he thought it was a penalty because he was that far away from it. I don't think he was close enough to give it."
Mellon insisted that up to that point his side had done enough to win the game. He continued: "We played all the football and made some good chances.
"They were limited to just the long ball forward. To lose in the fashion we did is so disappointing."