Armstrong, who rode 18th among the 180 riders to leave the start ramp, took the provisional lead early — baring his teeth and pedaling up out of the saddle as he neared the finish.

Only 15 riders later, Tony Martin of Germany outpaced him. Others also soon bettered Armstrong’s time, including Leipheimer and Liquigas rider Roman Kreuziger.

“Kreuziger just moved into 2nd. I raced with his dad! Haha,” Armstrong tweeted.

It was clearly an older Armstrong, not the Armstrong of old.

During his reign as Tour champion, Armstrong never finished lower than third in a time trial, except once, when he placed seventh in one in 2003.

“My heart rate — it didn’t look exactly at the top, probably 196 (beats per minute maximum), so that’s as hard as I can go,” he said.

In another time trial in 2005, Armstrong outpaced Cancellara by more than a minute.

Cancellara, of the Saxo Bank team, will wear the overall race leader’s yellow jersey for Sunday’s second stage — a 16.2-mile ride across plains from Monaco to Brignoles, France.

“I think maybe in 5 years there are other riders coming and they will be faster than me. That’s cycling — that’s time,” Cancellara said, when asked about Armstrong. “I also get older.”