"We didn't defend well enough in the first few league games – not just the back four but the whole team," Rooney is quoted as saying on United's official website. "But today, we were brilliant.
"They are a really big team, a physical team, so we knew we had to defend our box really well. We managed to do that.
"There was a focus about us today and we need to do that for the rest of the season if we're going to be successful."
United remain second in the league table with 15 points from seven matches, four points behind leaders Chelsea.