The News of the World columnist believes Liverpool's victory will also inspire the likes of Arsenal and Manchester City, who still have to visit United, which could lead to more home game horrors for Sir Alex Ferguson's men.
"Liverpool are back in it," said Dunn. "It hasn't blown the title race wide open but it has certainly turned a procession into a race again. It is also symbolic that United aren't untouchable. Steven Gerrard said afterwards that he thinks the importance of the result will be that other sides will believe they can take something from United.
"Liverpool need other sides to beat United in the run in and I think over the past two or three months teams have laid down in front of United. The fear factor has been so great teams like Fulham have gone there without any hope or optimism of getting a result, they've actually written the game off.
Pressure"This win shows that if you put United under pressure, the back four under pressure, the goalkeeper under pressure, they will make mistakes.
"United have got such great press for their defending but that's because they defend from the front, going forward. Yesterday they didn't do that. All of a sudden you are exposing (Rio) Ferdinand, (Nemanja) Vidic and (Edwin) Van der Sar to pressure, and they couldn't cope.
"If you look at them individually there are frailties there. The right back yesterday (John O'Shea) isn't a right back and didn't have a good game. Patrice Evra has had a great spell with United but when he started his career with United he was very iffy and did have a bit of a seeing to by Aaron Lennon in the Carling Cup final so there are frailties there.
"(Fernando) Torres and Gerrard put them under constant pressure and they were nervous. That is what Gerrard is saying - have a go at them."
Dunn also thinks comments by Wayne Rooney ahead of the game did nothing other than put pressure on himself to perform, which told through out the encounter. "I've got no problem with him saying he hates Liverpool - Liverpool fans would be offended if he said he didn't hate them!
"I think what it does is put a lot of pressure on Wayne Rooney. He was a really frustrated figure yesterday. At least three times in the first half he was having a real go at his team mates."
Benitez safeLiverpool supporters were, as always, desperate to overcome their bitter rivals and the memorable victory, says Dunn, will fend off any concerns the fans have about manager Rafa Benitez, for this season at least. "In terms of Benitez, it has cemented his standing amongst the fans," said Dunn.
"No matter what happens, even if they don't win the Premier League, they've beaten Madrid and Man United with four goals in the space of five days. There was a little undercurrent going against Benitez, I think that's gone."