This was just one hurdle too many, one obstacle too great for David O'Leary's fearless young side to overcome.

The vibrant adventure that has caught the imagination this season is finally over.

Experience, in the form of last season's finalists Valencia, has finally prevailed over youthful exuberance and promise.

Nothing can take away the memories, nothing can reduce the impact of the lessons which O'Leary's team will have had indelibly printed on their hugely promising careers.

However, while there was considerable controversy over Valencia's opening goal as Juan Sanchez appeared to use his arm to guide the ball past Nigel Martyn, the result was never seriously in any doubt.

That Sanchez, the player upon whom Lee Bowyer had stamped to be ruled out of this game through suspension, should have made it 2-0 just after the break, only added insult to injury.

But that Valencia's inspirational captain Gaizka Mendieta should have then scored a third shortly afterwards was, in terms of his own memorable performance of charisma and class, only just.

Leeds frustration boiled over completely at the final whistle as Alan Smith betrayed his questionable temperament by receiving a red card for hacking at substitute Vicente.

And that was it. Leeds' pitfalls of the past 18 months have been as serious as the deaths of two fans in Istanbul, a court case and retrial, as well as injury upon injury, and then the loss of Bowyer on the eve of their biggest game in 26 years.

Emerging from the qualifying round, they had also had to recover from a 4-0 defeat away to Barcelona that looked to have exposed them as virtual novices in their first Champions League campaign.

But they had still gone on to prove themselves against the cream of Europe - AC Milan, Besiktas, Lazio, Anderlecht and Deportivo La Coruna.

This, however, was just one step too far. After a goalless draw at Elland Road reduced their chances but retained some hope, they never gave up in Valencia.

They never would have done. But, in truth, they were comprehensively outplayed by a side who, as Manchester United, Arsenal and Rangers have found to their cost in the past two years, are a class act.

They have not lost in 25 European ties at Mestalla, stretching back to 1992 and have one of the finest club defences in the world and have the inspirational talents of Mendieta, Sanchez, Pablo Aimar and Kily Gonzalez.

Leeds were always struggling and they needed all the sense of togetherness imbued by their short-back-and-sides haircuts to resist an impassioned Valencia assault right from the kick-off.

Mendieta, who had been relatively quiet in the first leg, was Leeds' chief tormentor.

Indeed, he gave Harte a runaround he is unlikely to ever forget, with Nigel Martyn having to save his driven volley as early as the third minute.

For a while, the visitors looked to have weathered the early storm.

If only it had been true. For just as at Deportivo La Coruna in the quarter-final, they went behind amid some controversy.

This time, Sanchez, who had already headed over the bar, stole ahead of Rio Ferdinand to meet a cross by Mendieta after the Spanish international had again left Harte in his wake.

Stooping to connect, he missed the ball with his head and it bounced into the net off the top of his arm.

Leeds' protests were vehement, with Martyn resembling the incredulous figure of Peter Shilton at Mexico in 1986 after Maradona's 'Hand of God', but with the same lack of effect.

Now, more than ever, Leeds needed Harry Kewell, who has been shadow of his normal self since returning from injury, to produce.

There were certainly promising signs as he twice reached the byline, as well as sending a swerving shot just over the bar.

However, he never found that missing ingredient and, in the absence of Bowyer, Leeds were too predictable in failing to use the right flank.

It was left to Olivier Dacourt to try to inspire them from central areas, surging forward on one incisive burst, but half-chances came and went for David Batty as well as isolated strikers Smith and Mark Viduka.

Valencia continued to threaten themselves though, with Carew's deflected header and Roberto Ayala heading a corner just off target.

And there was no recovery from the sickening hammer blow which came just 100 seconds after the restart.

Leeds were guilty of losing possession and then failing to close down Sanchez as the midfielder was allowed to advance unfettered before unleashing a 25-yard drive into the bottom corner of the net.

The Mestalla was still a vibrant, buoyant sea of twirling scarves as Mendieta broke free again, only for his touch to let him down as Martyn rushed out to smother.

It provided the most temporary of respites.

Just a couple of minutes later, the Valencia captain made no mistake as Leeds' depressed defence parted obligingly again to widen the gulf between the sides.

It was all over bar the considerable shouting and whistling of Spanish celebration.

Sanchez hit the post later on, Mendieta's brilliance continued as only Martyn's reflexes denied him as well as John Carew.

O'Leary's side were left to battle on bravely but without ever any hint of a comeback, with Smith's red card leaving a bad taste in the mouth as the final memory of a spectacular campaign.

Leeds may have been outplayed, but they should remember that it took Sir Alex Ferguson five attempts to take United into the promised land of the Champions League final.

There may be considerable sadness in defeat so close to the final, but, overwhelmingly, there should be pride at what went before it.

So much for the strength of the Premiership over La Liga though.

Teams:

Valencia: Canizares, Angloma, Ayala, Pellegrino, Aurelio, Albelda, Mendieta (Angulo 73), Aimar (Deschamps 70), Kily Gonzalez (Vicente 65), Carew, Sanchez.

Subs Not Used: Palop, Djukic, Zahovic, Alonso.

Booked: Sanchez, Aimar.

Goals: Sanchez 15, 46, Mendieta 52.

Leeds: Martyn, Mills, Ferdinand, Matteo, Harte, Bakke, Dacourt, Batty, Kewell, Viduka, Smith.

Subs Not Used: Robinson, Kelly, Woodgate, McPhail, Wilcox, Burns, Maybury.

Sent Off: Smith (90).

Agg (3-0)

Att: 53,000

Ref: Urs Meier (Switzerland).