Manchester – Sir Alex Ferguson has fanned the flames ahead of Sunday's potentially explosive encounter between Manchester United and Liverpool at Old Trafford by dismissing his arch-rivals as one-season wonders.

Ferguson is still smarting from this fixture last season, when United took the lead only to capitulate to a 4-1 defeat in which Nemanja Vidic was sent off.

Liverpool lost fewer games than United last season and pushed their rivals all the way in the title race. Many expected them to come back even stronger this season but Ferguson insists he always viewed last season's vibrant challenge as a one-off from a side that had reached its peak.

Just to anger Benitez and his players even further, Ferguson has also hinted that the Merseyside club receive preferential treatment from the FA's disciplinary gurus in the wake of Steven Gerrard's escape from punishment despite his controversial challenge on Portsmouth's Michael Brown earlier this week.

As far as his assessment of Liverpool's on-the-field influence goes, history suggests Ferguson was correct, with Benitez's squad now struggling to secure a top four finish and Champions League qualification.

Ferguson, who could welcome back Ryan Giggs from a broken arm, said: "I thought it was an exceptional season and I thought it would be difficult to achieve that again. That was just my opinion.

"Did they over perform? Yes. I think they did very well. When they got that run going they showed form and consistency. That helps.

"I don't know what they are mired in. I think that their challenge last year was obviously championship form but sometimes a team peaks with that particular team and sometimes it's difficult to do again.

"It happened to me and, in my second full season, we ended up middle of the league.

"I think everyone expected Liverpool to be better but they are not and the challenge for them, along with a few others, is to get that fourth spot, which is a league of its own. I think we can all say with certainty that one of ourselves, Arsenal or Chelsea are going to win the league. But no one has any certainty about fourth place, it changes every week almost."