Sydney - Roads were being closed in Adelaide on Saturday to pen back the legions of Lance Armstrong fans thronging the usually sleepy Australian south-coast city for the return to competition of the seven-time Tour de France victor.

"For him to be here and racing in the Tour Down Under is unbelievable," said breathless admirer Allan Davis.

Davis, by the way, is no ordinary fan: he's finished high in the rankings of the six-day Adelaide event since it began 11 years ago and is this year's lead rider for the Quick Step-Innergetic Team.

"While the Tour Down Under has always been a sensational event to race in ... with him here, the hype has gone to a level I'd never imagined," Davis said.

Armstrong, 37, ends his three-year retirement from professional cycle racing Sunday in a 51-kilometre dash around the city streets for a cancer charity.

It's not the sort of race suited to an endurance athlete like Armstrong, but organizers predict 100,000 spectators will be behind the barriers for the twilight event.

Hosting what's called The Cancer Council Classic was one of the conditions of the world's most-celebrated cancer survivor deciding on Australia as the location for his first outing with the Astana Team and his first professional engagement since winning the 2005 Tour de France.

The Texan has been at pains to downplay his chances in the 800- kilometre Tour Down Under. With an average stage length of just
133 kilometres, and without the stupendous climbs of the European classics, it had Germany's Andre Greipel, a brawny sprinter who is slow on the climbs, as its victor last year.

"I still go in with modest expectations - mixed with nerves and excitement," Armstrong said of the stage race beginning Tuesday. "No major goals - other than to make it through and get back to the rhythm of racing."

Armstrong, who is using the Adelaide event as a springboard for the more arduous Tour of California next month, has impressed the racing pundits who have seen him on training rides. He romped up Willunga Hill, the course's biggest obstacle, ahead of his Astana team-mates and at 78 kilograms is close to his fighting weight.

Armstrong has had more than a dozen doping tests since September when he announced his plan to return to racing and try for an eighth Tour de France win.

He engaged Don Caitlin, one of the world's top anti-doping scientists, to independently test him during his comeback.

"It's formalized, it's underway, it's the most comprehensive anti- doping plan in the history of sport," he told reporters. "I'm proud of it, I respect Don. He's the toughest that's out there."

Many are convinced they are about to witness one of the biggest comebacks in sporting history.

It's actually Armstrong's second comeback; he quit in 1998, two years after beating cancer, but returned the same year.

"He's looking in superb shape," Astana manager and former professional cyclist Sean Yates said. "At this stage we haven't a game plan in mind, but let me assure you he doesn't want to look like a mug."

Australia's Patrick Jonker, who flanked Armstrong during his second Tour de France win in 2000, predicted the Texan would surge to the front on Willunga Hill, during the fifth and penultimate stage.

"What he'll do is up one of the climbs," Jonker said. "He'll show himself - he'll hurt himself and give it 100 per cent. That's just the way he is, isn't he?"

But noted cycling commentator Rupert Guinness was more circumspect, saying it was pie-in-the-sky to expect a clear run though the European classics and to July and the Tour de France.

"As invincible as Armstrong might appear, there are still serious obstacles ahead," Guinness said. "To be fair, he has been cautious about declaring what he can or can't do from next week onward." (dpa)