The Red Devils have netted 2.4 goals per game on average so far this season, a record which has helped them carve out a nine-point lead at the top of the table.
And Rooney believes that United must keep that run going if they are to overcome their porous defence and win the league.
“I can't put my finger on why we are not killing teams off,” he told reporters. “We have scored plenty of goals - it is the most number of goals we have scored at this stage of the season.
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“Maybe we are concerned with conceding goals, because we have conceded too many and have done throughout the season. But that is the way we are playing. That is the way we have been set up to play. We have to just keep our scoring going.
“Once you get an early goal the game settles down. We tend to win a lot more comfortably. When you go behind you end up fighting for the whole game. It can take a lot out of you as well. If you get an early goal it is great because you can see the game out without giving everything.”
The 27-year-old also insisted that his side are far from confirmed as title winners and called on his team-mates to remain grounded and keep picking up points.“The results are the most important thing now,” he added. “You look at City against QPR - they should have got the win, they had a lot of chances but they ended up dropping two points.
"That could quite easily have happened to us against Southampton. We had to dig in and hold on for the three points. Thankfully we got them.
“We have to keep taking each game as they come and picking up the points whenever we can. I am sure once it comes down to the last four or five games, then we will see what position we are in and work out what we have to do. But for the moment we have to take each game as it comes.”