Adelaide, Australia - Australia's Allan Davis fancied his chances of keeping the race leader's ochre jersey in Friday's 143-kilometre fourth stage of the Tour Down Under.

"If the chance arrives, I'll definitely have a crack, but the plan is to keep it simple," the 26-year-old said on the starting line. "Normal thing is a break will go with some guys who are lower on GC [general classification - or the leader board], and they'll contend the stage. Then we'll get ready for the big showdown tomorrow."

Thursday's stage was crucial to the outcome of the six-day classic with Germany's Andre Greipel forced to retire after dislocating his shoulder in a crash into a stationary police motorcycle at 55 kilometres per hour.

Greipel, 27, the defending champion and race leader going into the stage, is heading to Hamburg for further treatment to injuries that are to keep the Columbia rider out of the sport for at least three months.

Winds gusting at 85 kilometres per hour littered the course with broken branches and played a part in bringing down more than a dozen riders.

Almost half the field trailed in behind Davis and the leading riders, leaving some favourites with a deficit of 20 minutes with just two stages to go.

"No wind - that's the first bonus of the morning," Davis said. "Compared to yesterday, the last thing you want is to crash again."

Finishing second to countryman and Rabobank rider Graeme Brown, Davis was given the same time. Saxo Bank's Stuart O'Grady, another Australia, was lying third.

Seven-time Tour de France winner Lance Armstrong, in his comeback race after three years in retirement, is 29 seconds down on Davis and Brown in 39th place. The 37-year-old Texan was in a group of 16 riders who escaped from the bunch after 12 kilometres but failed to gel.

"We had 14 or 15 guys in the breakaway, but we couldn't get organized properly," Armstrong said, stressing that his first appearance in Adelaide was all about preparation for next month's Tour of California and eventual participation in July's Tour de France.

"Me being here is all about my own expectations and reminding people that it's a long season and that it's been three and a half years since my last race," he said. "That's a long time."

He tipped either Davis or O'Grady as the likely winner of the 11th edition of the Tour Down Under. (dpa)