Champions League fixture against Braga was crucial to their 3-1 victory.
The lights went out shortly after Alan’s 49th minute opener and the defender revealed that Sir Alex Ferguson made the most of the additional 15 minutes to inspire his team.
United had struggled to fashion many chances or any possession in the opposition half, and this proved to be the turning point.
When play resumed, Rio Ferdinand replaced Jonny Evans, and there was some crucial changes to personnel at important times in the game.
The additions of both Robin van Persie and Rafael proved pivotal to United stirring to victory in the last 10 minutes.
Van Persie managed to guide an 80th minute equaliser from outside the box, before Wayne Rooney converted a penalty, and Hernandez added a final goal to make it a 3-1 win and a flattering result for the Red Devils.
When asked about whether the lighting failure helped, Smalling told the Telegraph: “Yes, I think it did in a way.
“Especially after their goal. We knew we really had to pick ourselves up.
“We had a lot of the ball but we weren’t really getting anywhere. So yes, it really helped us.”
It was clearly viewed as a successful evening by United players in the end with defender Rio Ferdinand tweeting to last night’s birthday boy David De Gea: “Nice birthday present that, 3 points + qualified to knockout stages!”
Manchester United will be looking to build on their Champions League success when they visit Villa Park to take on Aston Villa this weekend.