They were chased by two riders from Contador's Saxo-Tinkoff team, Nicolas Roche and Sergio Paulinho, as they tried to increase the pressure on Froome's Sky teammates. Roche dropped off as they approached the first big ascent of the day.
Froome and Contador waited for the other one to show his hand. But neither did at first.
Van Garderen and Riblon reached the top of the next climb together, the Col de Sarenne, and braced themselves for a long and razor-thin descent.
In recent days, Froome had expressed concerns that the Sarenne descent, with its bumpy, pockmarked surface, was too dangerous. Riblon went off the road and, luckily for him, rolled onto a grass bank and not over the mountain.
"I have a lucky star over me," Riblon said.
Two days ago, Froome criticized Contador for riding too aggressively on a sharp descent to Gap, almost causing the Briton to crash. But Contador attacked Froome almost immediately down Sarenne, passing him on the outside like a Formula One driver.
Contador, joined by his teammate Roman Kreuziger, opened up a gap of about 20 seconds but lost that advantage after a few minutes. Contador's bad day was compounded when he had to change bikes.
Fans jammed the 21 hairpin bends on L'Alpe d'Huez in a chaotic atmosphere. Many were in fancy dress: Vicars, super heroes and other outfits of more dubious taste.
But there was still a degree of organization within the mayhem, with certain corners reserved for fans from certain countries.
One of those is known as "Dutch Corner" and several hundred screaming, shouting Dutch men and women formed a vortex that sucked the riders in amid a surreal cacophony of indecipherable shrieks, howls and wails.
Several dozen Norwegians, some in plastic Viking helmets, formed a human shield around one corner near the top. Elsewhere, a dozen or so Colombians marched uphill carrying a giant national flag.
Camping cars lined the hill, there were British Union Jack flags, Irish tricolors, Australian fans dressed in kangaroo suits and some dressed as inflatable giant flowers.
Occasionally, a distressed-looking police officer would blow a whistle, trying to stop fans from getting too close. One got too close to Riblon, who elbowed him in the chest, and a young boy ran in front of Froome, who just about avoided him.
Barricades were erected on the last part of the climb to give the riders some room.