Alan had handed Braga the lead before a floodlight failure caused the match to be delayed by 15 minutes.
After the teams returned, Robin van Persie, Wayne Rooney and Javier Hernandez all scored in the final 10 minutes to earn United a 3-1 win and Smalling has admitted that the delay played a crucial part in their comeback.
Smalling said: "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."
Smalling was playing his first game of the season after a broken metatarsal had kept him out of action since July.