The England international bundled home Joe Gomez's cross eight minutes from time but the substitute's celebrations in front of the Kop were cut short.
The ball had bounced off his chest on to his arm and referee Paul Tierney disallowed it after taking the advice of his assistant.
“I think it was very unlucky," he said. “There wasn't much I could do. The defender kicked it on to my chest, I tried to chest it in and it has clipped my arm. The referee disallowed it but it's very unlucky.
“I thought he had given it. I was celebrating for a while. I don't know what changed his mind, but he changed his mind.
“I thought I won it. It's not nice when you are celebrating and it gets disallowed. It was annoying but hopefully I will get a goal soon and carry on from there.
“It's always hard when a team tries to play so defensively, you have to try to break them down. We had a few chances which we didn't take. It was always going to be difficult but we have to learn from it."