Tony Gallopin rode away from a splintered peloton in the final two kilometres on Friday to continue the French winning streak at the Tour of Spain.
As the AG2R rider turned to look back at his distant pursuers in the finishing straight of the seventh stage, even he seemed surprised by the success of his attack.
His victory followed compatriot Nacer Bouhanni's victory for Cofidis in a sprint on Thursday.
Another French rider, Rudy Molard of Groupama-FDJ, added six seconds to his overall lead.
"If I had a chance, I wanted to try to attack. I found the best time to do it and I'm delighted," Gallopin told the television cameras immediately after the finish.
Gallopin has had a difficult year and was forced to withdraw during the Tour de France.
"It's a dream for any rider to win on a Grand Tour, especially after a season like this, so much bad luck," he said. "I often fell, I was sick. The plan was to come to the Vuelta and see if could I win a stage. So the plan was good."
In the frantic scramble for bonus seconds, Slovak Peter Sagan (Bora-Handsgrohe) edged out Alejandro Valverde (Movistar) for second place, five seconds behind Gallopin.
The Spaniard's small third-place bonus lifted him into second overall, 47 seconds behind Molard and one ahead of German Emmanuel Buchmann of Bora. Molard finished with the same time.
The largely flat 185.7-kilometre stage from Puerto Lumbreras to Pozo Alcon contained one booby trap, a third category climb followed by a twisty descent on rough roads, which tripped up several leading contenders including Michal Kwiatkowski (Sky) who started the day second overall. The Polish rider crashed on the descent and finished 30 seconds behind Gallopin.
Molard is the first Frenchman to hold the overall leader's jersey in one of the the big three stage races since the 2014 Tour de France when the Frenchman who briefly wore yellow was Gallopin.
Saturday brings another flat stage, over 195.1km from Linares to Almacen.