Benitez: United best opponents to bounce back
"It is the best way to do it," Benitez told a news conference on Friday.
"This game against United could be the right opportunity for us. It's a massive game against our rivals and the fans will be right behind the team from the first minute to the last minute."
Liverpool are enduring their worst run of form for 22 years and are eighth in the Premier League but Benitez said he was not worrying about his job, despite four successive defeats.
"I'm relaxed in terms of my position," the Spaniard said. "As a manager you know that you will have good moments and bad moments. At this moment we know that we have to improve, we have to win and it's a question of time.
"I'm sure once we have won one game then everything will change."
Liverpool, who have fitness doubts over Fernando Torres and Steven Gerrard, will fall 10 points behind Premier League leaders United if they lose again on Sunday at Anfield.
Torres has missed the last two games with an abdominal strain while Gerrard limped out of Tuesday's Champions League defeat to Lyon with a recurrence of a groin injury.
England full-back Glen Johnson is also a doubt with a groin problem.
"The three of them will be late decisions," said Benitez. "We have to decide tomorrow because they are training and working with the physios."