His flap which led to Spurs' late equaliser is viewed as a watershed moment in De Gea's United career.
"I look at that Tottenham game and I still think it was a good game (from me) even though I made a mistake at the end," he told the Daily Mail.
"But I was confident I was already getting better before that game. I had produced some good performances before and did so afterwards. During the tough times I always kept it in my mind to keep working harder to become a better player.
"I do not think people appreciate just how hard it was for me coming to a new country at that age and a different type of football but I am thankful to God that I have progressed even though it was hard.
"My immediate family came over with me from the start but I missed my friends back home. I know there was a stage when I was dropped to the bench, but that was good for me as it made me stronger and better.
"Also the trust that Sir Alex Ferguson put in me gave me a lot of confidence. He was like that with me from the very start.
"And Eric Steele was a great goalkeeping coach who always looked after me and I will remember that. Now I have a new coach and I am enjoying learning different things with him. Everything is now better. I am very happy in Manchester."