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6 a.m. on NBCSN — Stage 4, Mondorf-lesBains, Luxembourg to Vittel, France

Longwy, with a short very steep section, was testing enough to give an early inkling of the fitness of some of the top riders. Porte, who used to be a teammate of Froome’s at Sky before switching to BMC, impressed with his attack.

“It showed that he’s in great form and will always look to use his legs to gain some time,” Thomas said.

Porte finished the stage in the same group as Froome and Thomas — two seconds behind Sagan and other riders who went all out for the stage win. Porte, who is 35 seconds behind Froome overall, was pleased to test his legs.

“It’s good for the confidence just to have a bit of a crack,” Porte said.

Other overall contenders who finished in the same group included Nairo Quintana, a three-time podium finisher, former twotime winner Alberto Contador, and Romain Bardet, runner-up last year to Froome. A sterner test of their relative strengths will come on Wednesday on a tougher climb to the Planche des Belles Filles ski station.

For the moment, their main goal is not crashing and losing time. That was easier said than done as the pack picked up the pace toward the end of what otherwise was a fairly leisurely 132-mile ride through the dense forests and plunging valleys of the Ardennes, from Belgium, through Luxembourg to France.

The last hour “was a hell of a fight,” Porte said. “It was quite a dangerous tricky final, so it’s nice to get through that one unscathed.”

With his long hair, quick humor and taste for showmanship, Sagan is one of the Tour’s most colorful characters. His ultimate goal is to win, for a sixth consecutive time, the green jersey. It isn’t as coveted as the yellow one but is still a solid measure of overall strength.

For the moment, however, Sagan planned to allow himself a celebratory drink.

“You’ve got to celebrate every victory,” he said. “But if I drink alone they call me a drunkard. I prefer to drink with my teammates.”