Germany's Tony Martin took the stage win Sunday, and France's Tony Gallopin took the yellow jersey during an up-and-down Stage 9 in the eastern Vosges mountains.
Martin, a three-time world champion known more for time-trial dominance, showed that he could climb too; Italy's Vincenzo Nibali, who has been wearing the leader's yellow jersey, didn't lay a hard enough chase of Gallopin to keep it.
French media — delighted to see the country's first yellow jersey holder since Thomas Voeckler wore it in 2011 — reveled in the fact that Gallopin will lead France's most beloved race on the Bastille Day holiday Monday.
The 29-year-old German, meanwhile, said his stage victory might have been an "omen" for Germany's World Cup ambitions against Argentina — which it turned out to be.
Gallopin, of the Lotto Belisol team, said he'd been plotting a move for the yellow jersey since Stage 5 — when he positioned himself for a challenge because Nibali was unlikely to want to hold it all the way to Paris on July 27, when the race ends.
It's a lot of pressure to try to carry the leader's shirt so long, through the Alps and Pyrenees ahead.
But Nibali knows that Gallopin is unlikely to make it up the big climbs ahead, and the Italian didn't lose any time against his biggest rivals — highest among them, two-time Tour champion Alberto Contador.
Gallopin, by finishing about 5 minutes ahead of Nibali, easily erased his deficit to the Italian and now leads him by 1:34. Portuguese rider Tiago Machado is third overall, 4:08 back. But, like Gallopin, he is not considered a Tour contender.
"It's with great pride that I will ride on the national holiday day in the yellow jersey," said 26-year-old Gallopin, adding that he feared he may not keep it after an uphill finish at the super-steep Planche des Belles Filles on Monday. "It's a little bit scary, but I will enjoy the day."
"It was always a dream of wearing the yellow jersey," said Gallopin, who finished 2:45 back of solo breakaway leader Martin.
Contador finished safely in the main pack along with Nibali and is 4:08 back in ninth place overall.
They will resume their contest in the toughest stage so far — Monday's 161.5-kilometre (100-mile) trek from Mulhouse to the famed La Planche des Belles Filles, featuring four steep Category 1 climbs. The pack takes its first rest day on Tuesday.
"It was a tough day," Contador said, looking ahead to Monday. "We'll have to decide whether or not we try to attack or ride defensively."
The Tour paid tribute to those who died in the First World War — 1914-18 — by riding along the battlefields where millions died.
Sunday's route took the peloton past a landmark remembering the Battle du Linge in 1915, where some 17,000 French and German soldiers fell in three ferocious months of fighting. The groves and thickets in Le Linge's mountainous pass helped mask lethal sections of barbed wire protecting tight German defensive lines.
Shortly before the day's most difficult climb — a Category 1 ascent of 10.8 kilometres (6.7 miles) up Le Markstein — Martin broke away, and Gallopin's chasing group was about two minutes behind with Nibali more than six minutes adrift.
Martin, some 18.5 minutes back, was no threat to Nibali's yellow jersey.
Nibali lost more and more ground, and urged his Astana teammates to step up the pace as they reached the last of the climbs — a short, sharp ascent up Grand Ballon. But they left themselves with far too much to do.
Martin, who narrowly beat Tour champion Chris Froome in a time trial last year, continued to surge ahead, with tail winds making for a quick descent down to the finish. The departure of Froome in Stage 5 due to injury has blown the race wide open.
AP Sports Writer Jerome Pugmire contributed to this report.