Television replays appeared to show Diamanti first touched the ball with his right foot as he slipped on his approach before slamming the ball into the roof of the net with his left.
But he insisted: "I don't care what TV shows. It deserved a goal. I don't believe I touched it twice. I was trying to hit it down the middle and that is what happened."
It was Diamanti's first start following his arrival from Livorno.
He added: "It was a really hard match. We knew what to expect.
"It has been a month that I haven't started a match. I am so sorry for the fans that we lost because we played well as a team. I am sorry they managed to score in the end."