Gabriel Obertan struck the only goal of the game midway through the second-half.
Ferguson was pleased that his side were able to build on their 3-1 victory against Celtic in their opening tour match on Friday.
He said: "You need pre-season games, they are absolutely essential. You need them to get your timing and rhythm and your breathing right.
"It was the sort of game we probably needed. The Union were really powerful and aggressive, got to the ball quickly and made it difficult for us. They had a few shots on goal. They were better than I expected.
"We increased the tempo in the second half and did a little better then. It was a good game for us. They were very good opponents, I thought they did really well."
It was United's first visit to the stadium since 2004 and the match had the feel of a cup tie thanks to an enthusiastic crowd of 44,213.
Ferguson said: "There was a more United atmosphere for us tonight. In the six years since we were last here there is more appreciation of the game from the fans in what is happening on the field.
"It is an indication of the progress there is in American football."