The American was the last of the 189-strong field to set off and blazed around the 7km course in nine minutes eight seconds to beat France's Laurent Jalabert by two seconds.

Lampre rider Raimondas Rumsas, of Lithuania, was third in 9:11 with Colombia's Santiago Botero, the Kelme team leader, back in fourth in a time of 9:12.

Britain's David Millar, who won the prologue on his debut in 2000, was fifth in 9:13.

US Postal rider Armstrong, who will wear the leader's yellow jersey for the first road stage, last won the prologue in 1999, the year of his first Tour de France victory.

But last year's prologue winner, Christophe Moreau, of France, trailed in well down the field in a time of 9.32.

Australia's Bradley McGee was one of the early leaders but as the hilly, partially-cobbled street circuit dried out, his time of 9:21 was consistently bettered.

Armstrong, setting off at 1808 BST in overcast but dry conditions, rode the course at an average speed of 42 kilometres per hour.

It was his 12th stage victory in the Tour and his seventh in an individual time trial.

The Texan also won the Dauphine Libere and Midi Libre cycle races this season.

Meanwhile, the 25-year-old Millar, riding for Cofidis, will wear the white jersey on stage one for the best young rider.

And Jalabert, last year's King of the Mountains, has the green jersey.

Sunday's first-stage-proper is a 195 km circuit in the countryside around Luxembourg.