Shame Dublin’s indie-boy intelligentsia, who have been delightedly covering Justin Timberlake’s debut single ‘Like I Love You’ at every gig, aftershow and lock-in for months, aren’t here tonight: it’s a great opportunity missed, in more ways than one. “This is the biggest contingent of ladies I have ever seen at a gig,” notes my musician friend, craning his neck like a fox at a chicken ranch.

Of course, they would have had some extremely serious competition. “Is there anybody out there tonight who would be my girlfriend?” enquires the world’s most famous jiltee to earsplitting shrieks, resplendent (for now) in sleeveless boy-band white, his improbable, genetically-engineered posterish perfection offset by a Madonna-style headset-and-mic curling round on one side. And no, it’s not a prop, he is singing live – but, wow, for the first few numbers, Justin Timberlake is nervous: a close-up on the overhead screens as he jauntily bounces through current single ‘Rock Your Body’ reveals a faraway expression in his eyes, as if he is concentrating on some long-past reminders from his choreographer.

The poptasticness of the whole thing is both thrilling and damn weird. First, there are the backing dancers, who flounce Fameishly across an immense multi-level set, loping into and out of Michael Jackson-patented pyramid formation, playfully sidling up to Justin and then (art imitating life as it does) sashaying out of his arms again as he reaches for the next temptress-from-the-block. Then there are the costume changes: if you didn’t like Boy-Band Justin (white onesie), you might very well get into Alterna-Cool Justin (black leather), you’ll go all unnecessary over Ghetto-Fabulous Justin (black satin Adidas tracksuit) and you’ll be plumb crazy about, er, Hunting-Lodge Justin (houndstooth trousers; peaked tweed trilby; smart waistcoat). Then there are the pyrotechnics, booming and flaring brilliantly at the end of each track (fucking cool!). It’s like being at the circus, but with kicking tunes.

And this is the real reason why tonight is such an unqualified triumph: the songs – already on a par with Jacko’s best singles thanks to writer/producers Timbaland and Pharrell Williams – are bolstered by the most extraordinary musicianship this side of the Montreux Jazz Festival, not least from Justin himself, who is brilliantly note-perfect throughout. A slapping, sharp drumkit galvanises an electrifying ‘Like I Love You’; congas and brass caress ‘Nothin’ Else’ into a bruisingly lovely sunrise of Innervisions soul-jazz; and the revenge-black hip hop of ‘Cry Me A River’ gets kung-fu-kicked with post-Buffy heavy-metal beats before a phalanx of throatily soulful singers lead it into its dark-blue denouement. As for the flawless three-way jam with his drummer and DJ, with Justin himself on human beatbox – well, even Grandmaster Flash himself, playing across town tonight, would have shaken his hand.

Britney would have fucking hated it.