Here is a well balanced article that eplains the demise. This is why I like to read The Guardian (most times) and they are traditionally ManU haters.
http://football.guardian.co.uk/Match_Report/0,,2071191,00.html United collapse as Kaka leads Milan to Liverpool rematch
Kevin McCarra at the San Siro
Thursday May 3, 2007
The Guardian
Manchester United came to San Siro shimmering with hope that they would wrest triumph from Milan. In the end all they could take away was the grim comfort of knowing that they could have done no more against stylish and shrewd rivals who had outclassed them. There is to be no Champions League final between Premiership clubs. The Athens police will be relieved not to have the prospect of United and Liverpool fans duelling on their streets, and for the rest of us there is another sort of reward.
On May 23 Milan will seek to settle accounts with Rafael Benítez's squad, who tore the trophy so audaciously from their grasp in 2005. Events here must fire a conviction that they have all the arts required to do so. It will, none the less, be an utterly different affair to this semi-final. Liverpool thrive on their defence whereas United, so understrength in that department, could not prevent a refined devastation by Milan.
Sir Alex Ferguson's team may have shaken off a spell of domination from Carlo Ancelotti's footballers last week to pull off a 3-2 win but there was no escape here. Benítez will dwell on a stretch of the second half at San Siro when Milan, 2-0 ahead, were reduced to hacking the ball away in an unrefined way. Wayne Rooney, then, was even demanding a penalty as he was jostled while attempting a bicycle kick.
Despite all that Liverpool's manager will also jot down the fact that United did not force the goalkeeper Dida to a truly testing save. The lesson for United, such as it was, had probably been taken on board weeks before kick-off.
Ferguson had grasped the fact that a makeshift defence will not do when a midfield as balanced and creative as Milan's is out to undermine it.The United manager tried to hearten his players by making light of the jeopardy,
making it clear that a goal for Milan was to be expected. He was only imploring the heavens that there would not be a string of them. The Italian side, though, grew ravenous for goals
when they realised how immobile poor Nemanja Vidic was. The Serb was the centre-half lured into a premature comeback, after a month out with a broken collarbone, because Rio Ferdinand was ready for no more than a seat on the bench.
United's creative players floundered for the most part
but how could they set about Milan with poise when there was forever a chance of imminent disintegration behind them? At a minimum the Old Trafford club would have given Milan a far more stringent examination had their squad been as near to full strength as Ancelotti's.
In reality the latter's men could put on an exhibition of their artistry from the outset. The thunder rolled and the rain gushed down to make the surface slick but Milan's football was slicker still. Vidic's frailty was caught in the searchlight of some blinding moves as the members of the Serie A club's exalted midfield vied to outdo one another.
In the second minute Kaka had run straight past Vidic to slant a low ball across the face of goal which eluded everyone. Almost immediately Edwin van der Sar was saving from a revitalised Clarence Seedorf. This was a perfectly harmonious ensemble, with Rino Gattuso and Massimo Ambrosini catching the eye as they went about the everyday chores with efficiency.Milan were in front after 11 minutes when Seedorf headed down a long ball and Kaka, from 22 yards, drilled a low left-foot shot past Van der Sar. The goal was simple yet crammed with understanding and technique. There were no such demonstrations from United before the lead was doubled.
After 30 minutes Gabriel Heinze played a foolish pass to Vidic and the Serb cleared only as far as Andrea Pirlo, who squeezed over a cross. Vidic met it with a tame header towards Seedorf, who forced himself away from Darren Fletcher. The Dutchman then skipped wide of Vidic's sliding attempt at recovery before picking the same spot as Kaka.
United often carried the game to the opposition thereafter but not in a manner to make Ancelotti panic. There was little more than an impression, at the start of the second half, that the tempo was causing Milan a certain amount of discomfort. None the less United could have gone three down at that juncture.
Kaka, in search of his fourth goal of the tie, had turned inside Vidic in the 53rd minute and drawn a good parry from Van der Sar. In sitting deep Milan also proved that they had been studying the causes of their decline at Old Trafford. Here Wayne Rooney and Cristiano Ronaldo could expect clusters of opponents around them whenever they got the ball and they allowed themselves to decline into counterproductive frustration.
Milan established the 3-0 lead in the 78th minute. Ambrosini's pass from the left on the counterattack was exquisite and the substitute Alberto Gilardino hared through to flight a finish past Van der Sar. United had dreamed of attaining greatness at San Siro but will now fix their minds on the Premiership title and the FA Cup.
