"We know how difficult it is but if we do our best and win, when the time comes for us to face Arsenal and Chelsea, who can say how close we will be? They know it's always going to be difficult for them when they come to Anfield," he said.
And Benitez admitted that a win against United could prove an important psychological benefit to his team.
He said, "When you beat the big teams, nothing seems impossible for the rest of the season. When people talk about the gap of 19 points to United or 37 points to Chelsea, there is an immediate way to cut this. You can reduce the gap by six points in just one game. If we win, it's three points more to us compared to last year and three less for them. That gap can be reduced."
And Rafa admitted he is hoping to create better memories of facing United, following disappointing results last year.
He said, "I have bad memories of playing Manchester United last year. We conceded two goals from setpieces at Old Trafford early in the season when we had some new players and we lost at Anfield because of a mistake."
"I remember it was tough, but I think we have a better side now. I think we are more familiar with each other and our system now, and our coaching staff know more about how United play. We had some players like Morientes and Pellegrino making their debut against them last time, so it wasn't easy," he said.
Rafa added, "This time we are going into the match with a lot of confidence. We have three clean sheets and two points away from home. That's not bad, but we know we need to start scoring goals. We've done that in midweek, so that shows that's not going to be a problem."