United, playing only their second game since early December after a spate of postponed games, certainly looked rusty as Derby moved off the bottom of the division despite their 21-point deductions earlier this season thanks to Tom Lawrence’s brace of impressive individual solo goals.
United dropped to 14th at full-time, and are now 10 points off the play-offs – with three games on hand on sixth-placed Boro, who are still to come to Bramall Lane.
And Rooney, who admitted he “feared” for his side today after they lost Graeme Shinnie and Phil Jagielka on the eve of the game, said: “Since the change of manager they’ve been In good form and we knew it was going to be difficult.
“The manager and coaches are doing a fantastic job there but we took away their qualities today, made them go a bit more direct and battled against them.
“We felt that was the best way to win the game. I think they have a chance of making the play-offs. They have some very good players and if they keep showing the form they have done they’ve got a very good chance.”
United’s best chance of the game fell to skipper Billy Sharp, who headed straight at Derby goalkeeper Ryan Allsop after a long throw was flicked into his path at the back post.