Teresa Carreño Youth Orchestra of Venezuela, Vásquez, Royal Festival Hall

It's now 21 years since I first heard the then-untrumpeted protégés of El Sistema, the Venezuelan phenomenon which has launched a thousand youth-and-music projects worldwide.

On that occasion the Royal Festival Hall was less than a quarter full, but we happy few all stood instantaneously for a work I'd never heard before (Estévez's Cantata Criolla, due for a comeback now). Last night it was a packed auditorium of all ages and sizes which gave a standing ovation to a symphony by Chávez - and that was just the end of the first half.

It's now 21 years since I first heard the then-untrumpeted protégés of El Sistema, the Venezuelan phenomenon which has launched a thousand youth-and-music projects worldwide. On that occasion the Royal Festival Hall was less than a quarter full, but we happy few all stood instantaneously for a work I'd never heard before (Estévez's Cantata Criolla, due for a comeback now). Last night it was a packed auditorium of all ages and sizes which gave a standing ovation to a symphony by Chávez - and that was just the end of the first half.

Much the same happened last year when the Simón Bolívar Youth Orchestra came to the Southbank for a residency and opened its rehearsals for free to ecstatic school parties. But the whole world wants that top team, so this time it was the turn of its not-so-little sister, the Teresa Carreño group, and the conductor was not the eminently marketable - and thankfully already top notch - Gustavo Dudamel but a 26-year-old of modest demeanour called Christian Vásquez.

I knew it would be no patchy second best at their second Southbank concert this week, not just from Kate Connolly's Berlin preview on theartsdesk but because I'd heard Vásquez conduct the SBYO in Lucerne after Abbado and Dudamel. The seemingly effortless way he inflected a Dvořák Slavonic Dance in a morning of children's pops was enough to inspire total confidence. And so it proved with another overwhelmingly large group, this time of 14 to 19-year-olds, with just as many double basses as big brother (13) and two tubas, yet a big band capable of being very nimble on its feet.

Vivacity hit us between the eyes right at the start with Bernstein's Candide Overture. There's no reference to the Voltairean hero's discovery of El Dorado in the curtainraiser's tune-parade, but the vast array of cellos (pictured right in rehearsal with some of the double-basses) smoothly sang their hearts out in the lovers' "Oh, happy we" - why does it always sound better here than on voices? - even if the violins were taking a bit of time to come into focus. That they did, and how, in the Chávez parade of Mexican folksong, his so-called one-movement "Sinfonia India".

This was Vásquez's first chance to show how nimbly he could negotiate tempo changes and accelerandi, both of which he did with a master's touch. The percussion and brass, which had already had a chance to shine in Copland's catchy El salón México - and set a child in the choir seats bouncing with excitement - let rip in a snaky final processional anticipating one of the Venezuelans' trademark encores. We duly got that later - the final dance from Ginastera's Estancia - but the exhilarating similarities accounted for both the premature and the eventual standing ovations.

After a buzzy interval, it was time for the serious stuff - the Tchaikovsky which has always sent the Venezuelan crowds wild: Dudamel told me when I interviewed him for Deutsche Grammophon how the audiences rush up in Caracas and shout for the finale of Tchaikovsky's Fourth as an encore. This was the Fifth which the Simón Bolívars have already recorded under their icon, and the TCYO/Vásquez experience, similar in approach if no mere carbon copy, was just as thrilling. I've heard few performances from the world's top orchestras which lift the first movement's Allegro con anima so engagingly, and absolutely none - not even the famous Leningrad/Mravinsky partnership - which digs into the finale's march-mania with more hair-raisingly trenchant articulation.

If, like Dudamel, Vásquez tends to veer between brilliantly fast and searingly slow, he does it with style - and that's a young man's prerogative. He tried out his new-found authority by holding the silence between first and second movements, run together with hardly a break, and for even longer at the end of the slow movement, after which mid-term applause seemed just fine. And that famous Andante cantabile unfolded with assurance, lashings of love and one astonishing billow from bottom to top of the string section; the scherzo-waltz lilted with phenomenally clear execution of the tricky violin runs at its centre and it's not often that the euphoric ending brings tears to the eyes. Again, the standing ovation was instant.

It was rewarded with three encores. I'd have liked, on the first-half evidence of two solo trumpeters in the Copland and the Chávez, to have heard the mariachi effect on the Neapolitan Dance from Swan Lake. But by now the crowd expected its Latin rip-roarers, so we got the never-wearing brass struts (pictured left in rehearsal) and string-instrument spin-arounds in Tico-tico by one Abreu - not the man who founded the Sistema, José Antonio, who as Sir Simon Rattle rightly says deserves next year's Nobel Prize - the splendidly ubiquitous Ginastera and the equally predictable but ever-welcome Bernstein West Side Story Mambo, shorn of its threat in context and turned into an irresistible audience-participation party piece. There aren't many concerts in a lifetime of which you can happily apply the cliché that you came out feeling the world was a much better place, but this was certainly one of them. Come back soon, please, you Teresa Carreños: our country needs to see more of your disciplined sense of vocation as well as your joy.

Watch a fledgling TCYO under Dudamel in Aldemaro Romero's Fuga con Pajarillo:

• Find Gustavo Dudamel's Tchaikovsky Fifth recording with the Simón Bolívar Youth Orchestra on Amazon
• See what's on at the Southbank Centre this season
• More about the Southbank's Sounds Venezuela series