Toulouse, France ? Lance Armstrong’s struggle to dominate a surprisingly difficult Tour de France could hinge on beating the clock in today’s individual time trial — a decisive race on undulating terrain.

The four-time champion holds the overall lead in this year’s Tour, but only by 21 seconds. Unlike past years, his top rivals feel victory is within their grasp.

“The standings are very close,” Armstrong, soaked in sweat, conceded to reporters Thursday.

None of the Tour’s top contenders, including American Tyler Hamilton, who is competing despite a broken right collarbone, bothered to mount a challenge Thursday on one of the Tour’s least punishing stages.

Instead, they rode alongside Armstrong on the flatlands from Narbonne to Toulouse, always staying within the main pack and finishing in the same time.

Alexander Vinokourov of Kazhakstan, 1997 Tour winner Jan Ullrich, Spanish rider Francisco Mancebo, Iban Mayo of Spain, and Hamilton chose to conserve their forces, hoping to chip away at Armstrong’s lead during Friday’s vital individual time trial.

“The time trial is totally going to dictate how the rest of the Tour is raced,” said Frankie Andreu, a former U.S. Postal Service teammate of Armstrong who follows the Tour closely.

The 29-mile run across the sun-drenched hills from Gaillac to Cap’Decouverte is raced against the clock and riders leave several minutes apart.

Armstrong has acknowledged the stage — the Tour’s 12th — poses the toughest challenge since he first won the Tour in 1999.

Thursday’s 11th stage gave lesser-known riders a chance to grab the spotlight. Armstrong finished 42 seconds behind the winner, Spanish rider Juan Antonio Flecha, competing in his first Tour. Dutch cyclist Bram De Groot finished second, and Spanish rider Isidro Nozal was third.