Two goals from corners in the first half took the Red Devils out of sight, and Tom Cleverley’s cross-cum-shot rounded off an excellent display from the visitors.
And, after seeing Rooney excel in an unfamiliar midfield role as United dominated, the Scot had kind words for the former Everton man.
“He’s getting fitter all the time,” he told Sky Sports.
“He needs the games obviously. With about 20 minutes to go I could see signs he was starting to tire a little but he’s put so much work into it. Some of his football was terrific today.”
The 70-year-old went on to praise his side's concentration and defensive steel at the Sports Direct Arena, a ground where they suffered a 3-0 defeat last season.
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“Last time we were bullied off the pitch and second to every ball last year but tonight it didn’t happen.
“The second half against Tottenham we were terrific; an absolutely brilliant performance. But the first half spoiled the whole day, but today the whole game we were really on top our game in terms of concentration, determination, all the things you want to see.
“Concentration is important at this level and we concentrated on the way we played first 20 minutes. It’s strange as we played such good football and created a lot of openings but scored from two set-pieces. That’s unusual for us but we’ll take it anyway.”
United host Stoke after the upcoming international break and Ferguson underlined the importance of getting a result to keep in touch with Premier League leaders Chelsea.
“You don’t want to fall too far behind,” he said. “If we hadn’t won today we’d have been seven points behind Chelsea. We’re in the frame, we’re still there and every game is important now because you want to stay up there and hopefully we can do that.”