The Dutchman had to be alert to goalbound efforts from Victor Moses and James McCarthy in the opening stages of the game, before making a fingertip save from Maynor Figueroa soon after the restart.
Sir Alex was pleased with his side's second half performance, but was keen to point out that the Reds' owed a lot to their goalkeeper.
"His composure is just outstanding as is his organisation of the defenders," the boss told MUTV afterwards. "Wigan were terrific in the first 20 minutes and Van der Sar had to make some great saves, while Vida and Smalling had to keep sticking their heads in to clear things. It was an uncomfortable time for us.
"We played really well in the second half and had some fantastic opportunities. We opened them up time and time again and could have scored more. But I'm happy with 4-0."
Two of United's four goals came from Chicharito who has netted in all four of United's league victories away from home this season.
"The boy is doing fantastic," added Sir Alex. "They were two good finishes. If you watch the first one again he bends his run and spins across the defender to the front post to knock it in. He made a great run for the second and Wayne played him in nicely."