At first, the crowd didn't seem to mind too much. After all, this was the first date in Winehouse's keenly anticipated summer tour of European festivals, which were to include gigs in Greece, Spain and Switzerland.
And the show on Saturday night was to have marked a glorious return for the troubled star, who has just finished a stint in rehab. They tried to make her go to the Priory, and this time she said yes, yes, yes.
A long-promised album from Winehouse had failed to appear in the shops. A shaky performance in Dubai four months ago was cut short following booing from the audience.
Yet by Saturday, apparently, the 27-year-old star was clean and sober, back on top of her game. This was to have been her triumphant comeback — and many Serbian fans had saved to buy their tickets in good faith.
They were £35 (Dh208) each; a significant sum when the average wage is £265 a month.
The lights dimmed. Eventually, a slight figure appeared onstage. She wore a tiny dress, tighter than a banana skin, her demi-beehive piled up like sooty candy floss.
After giving one of her backing singers a glassy-eyed hug, Winehouse sat down and took off a shoe. Looking confused, she stood up, bawled out half a song and then fell down. She got up again.
"Hello Athens," she said to the Belgrade audience. Later she seemed to think she was in New York. She left the stage for ten minutes and came back to caterwaul some more, then throw away her microphone before unravelling in front of a local audience of 20,000 and a global audience of millions.
Yes, the awful footage is all over the internet; a sad testament to one woman's hopeless addiction.
On Sunday night, an official statement was released saying that Winehouse has cancelled Monday's concert in Turkey and tonight's performance in Athens. Apparently, the singer feels she "cannot perform to the best of her ability" and will return home to recover.
In the end, Winehouse left the stage in disarray, with the boos and jeers of the audience ringing in her ears — appalled local journalists described the show as a "scandal" and a "disaster".
The question is: how much longer can Amy Winehouse go on like this before she kills herself?
Yet isn't there a manager or a single, responsible adult in her entourage who might say: "Okay, I cannot stop you abusing yourself, but I can stop you going onstage."
But what about a moral responsibility to the young girls who admire her and want to copy her? Those who ape her look and who see her, staggering around out of her box, and think that she still looks cool and daring. Her influence is pernicious; she is the toxic role model to end them all.
After all, thousands of young men admire Pete Doherty, the heroin addict and musician in jail for possession of cocaine.
The former Libertines singer is due out of prison on August 21 — and five short days later he is scheduled to perform at Leeds Festival in front of thousands of music fans. No, there is no shame in public life anymore, with fashionable stars such as Doherty or Winehouse forever forgiven their trespasses as they cling to bar stools in the last-chance ranch.
Winehouse is a junkie, someone who has to hit rock bottom before the long haul back to sobriety. Will being booed in Belgrade be enough to do it?
Addicts like her are not helpless people. It takes drive and organisational skills to keep your supply lines when you are abroad. And her particular problem is that being in a rock 'n' roll band only encourages a drink-and-drug-fuelled lifestyle.
Winehouse makes it her business to keep people around her who will allow her to carry on. That is her misfortune and also her fault. Whatever happens next, this concert was a seminal moment in her career. Who will take a risk on booking her now, even though she hopes to return to pick up the pieces of her shattered tour on July 8 in Spain?
All those promises of sobriety, all those hopes for the future, all turned to dust in a career-melting moment on a concert stage far from home.
Winehouse has lost the ability to moderate her life. Her tragedy is that she works in an industry that tolerates and lionises people like her and doomed Doherty.
Our tragedy is that so many young people idolise them.