Liverpool humiliated Man United 4-1 Saturday at Old Trafford in a statement victory that may sustain the Merseysiders’ title ambitions: fact.

For United, losing soundly to their most fierce rivals at home couldn’t have been better timed or circumstanced: thesis.

Yes, Manchester United were cruising.

They had just vanquished their manager’s biggest rival in fellow European giant Inter Milan midweek to advance to the quarter-finals of the Uefa Champions League. They’d won the Carling Cup and were through to face Everton in the semi-final for the FA Cup.

In the top flight, their dominance throughout the last five months is well-documented: unbeaten since being similarly dominated at Ashburton Grove in November, keeping 14 clean sheets in the EPL through December into February.

So as the Red side in Manchester entered play Saturday against Liverpool—seven points ahead of their nemesis with two games in hand—the timing and context couldn’t have been more perfect for a shocking upset.

Looking at the table, they could certainly afford it. Looking at individual player form, some could certainly use it.

The best player in England this season, Nemanja Vidic, has looked suspiciously shaken—at times—during a few of United’s last matches: home to Liverpool here, Inter during midweek, and against Fulham ten days past.

Easily the most consistent and effective player for United this season, the Serbian was execrable against Liverpool. “Monster” was solely culpable for Torres’ goal and was ultimately sent off for a shoddy professional foul on the Spaniard.

Vida will need to be focused and characteristically unforgiving during the run-out of this season for his club to unprecedentedly capture the three remaining trophies.

Both Vidic and lesser partner Rio Ferdinand enjoyed accomplished individual campaigns last season when Ronaldo rose above everyone to inspire United to the European double. The winger’s form this year, though, has also plateaued far below his potential.

His lack of confidence is apparent each time he plays the simple side pass after a few perfunctory step-overs, where last season the Ballon d’Or winner simply drove past and through defenders without thinking or pausing. His problems are mental.

Elsewhere, Michael Carrick, who has been largely consistent and influential this season, has slept through a few games on end, and serviceable players last year like Anderson and Nani have yet to find the form this year to emulate their effect past.

Patrice Evra has also not lived up to the high standard he set last season. Since serving a three-match ban over the holidays, returning splendidly at home to Chelsea, and then missing two weeks with a leg injury, Evra has not been at the races since.

Carlos Tevez was more effective than an inconsistent Wayne Rooney last season. The Englishman entered this season with a mind to prove his world-class hype justified. He’s yet to do it. His inconsistency is unrivaled by anyone on team. Rooney has a high ceiling but his form usually dwells far, far below it.

It’s unlikely he’ll admit to hating any future opponents.

There’s no doubt United players will be devastated with this result and rightly so. It’s the rebound to that emotion that can fuse the side together finally into the season’s business end. United manager Alex Ferguson nailed it home: “At this club it’s always about how you respond. When you lose a game: respond. And that is what we will do.”

If United had breezed past Liverpool just as they breezed past so many opponents in the last several months, the reality check could very well have come on a stage Manchester couldn’t afford.

But, being pummeled by their emotional rivals in the league—where United still lead by four points with a game in hand—brings stark reality and emotional checking far greater than merely dropping points against a lesser side home or away domestically and much less risk than sleep-walking over-confidently into a rampant European side.

Had the Mersey Reds nicked the victory, the psychological damage might not have been too severe, but, Liverpool might have just beaten Manchester United too severely Saturday.

Just as Rafael Benetiz’ factual tirade against Ferguson in December helped launch United on their recent domineering run, his side’s demolition of the Red Devils Saturday could very well be the impetus United need to continue their surge into history.

The victory that Liverpool reds will rely on as being the rebirth of their season could prove ironically to be the harbinger that refocuses their most ardent rivals from Manchester—clearly the better and deeper side this season—to trump them throughout England and Europe.