Rooney said: "The defence was brilliant, as they have been all season, so hopefully that will continue.
"We did that just before half-time and it put us in a good position in the second half.
"We knew Roma would come out and attack us and it created a bit of space for us. We had the two counter-attacks and made them count."
Rooney has now struck six goals in seven games against Italian opposition since April last year but he refused to get too carried away.
"It was a good professional job to come here and play well, and it gives us a good platform for next week," he said.
"With the Champions League you never know so we'll have to go out focused and with a good attitude and then hopefully we'll see the second leg through."