Michael Rasmussen's grip on the Tour de France yellow jersey will face the acid test on Wednesday when the race heads up to some unfamiliar territory on the 16th stage.
The third and last episode of climbing in the Pyrenees ends on the high, winding road of the Aubisque mountain pass.
Adding spice to the anticipated battle for command of the race is the fact the Aubisque, a 16.6km monster at an average gradient of seven percent, has featured only once as a summit finish.
In 1985 Irishman Stephen Roche claimed the honours, although it was legendary Frenchman Bernard Hinault who won the yellow jersey in Paris to secure his fifth and last triumph.
The battle for this year's yellow jersey could however be launched well before the main favourites reach the day's fifth and final climb.
And there's a good chance the Discovery Channel team of Alberto Contador, who will begin the stage 2min 23sec behind Rasmussen, will be the ones to light the spark.
Contador helped produce some of the most exciting racing the Tour has seen in years when he attacked Rasmussen four times on the way to Loudenvielle on Monday. The 24-year-old Spaniard didn't shake the Rabobank climber off, but Rasmussen showed signs of weakening.
The Dane, who is still shrouded in controversy over revelations of missed anti-doping controls, admitted his Spanish rival had him on the ropes: "I was really on the verge of giving up."
Nevertheless, a deficit of 2:23 - even going into a stage which includes two unclassified-graded climbs, and two slightly easier category-one ascent - is still significant.
But Contador is bullish about his chances of victory.
"I've got nothing to lose, and I'll be doing everything I can to put on a show, whatever the result," said the Spaniard. "If I can get to the time trial with just one minute of a deficit (on Rasmussen), I will have a chance."
Saturday's penultimate stage is a relatively flat 54km time trial which should suit the likes of Australian Cadel Evans - third overall at 4:00 - more than Contador or Rasmussen. That means Contador, and Evans, would have to take time from the Dane on Wednesday's 16th stage if they were to have any chance of upsetting Rasmussen on Saturday.
Legendary team manager Cyrille Guimard, who has produced numerous yellow jersey winners over the years, believes an attack early into the stage by Contador would be "suicidal".
"He (Contador) has a few options. They could try and isolate Rasmussen by using riders like (Yaroslav) Popovych and (Levi) Leipheimer," said Guimard. "They could also make sure they have riders on the front, protecting Contador from the wind in the valley. And they could start attacking from the foot of the Aubisque, which is long enough and has difficult enough gradients before and after Gourette," added the Frenchman, in reference to a turning point on the climb five kilometres from the finish line. That is where the riders usually collapse."
© AFP 2007