ANDORRA LA VELLA, Andorra—Sepp Kuss couldn’t suppress a wide grin as he raced toward the finish line to become the first American in 10 years to win a stage at the Tour de France. Just before winning Sunday’s grueling 15th stage, Kuss threw his sunglasses into the crowd and put his arms in the air before covering his face, succumbing to emotion and exhaustion. Tyler Farrar had been the last American to win a stage at cycling’s biggest race in 2011. “It’s incredible, I’m lost for words,” Kuss said. The 26-year-old Colorado native left it late to make his move in the punishing 191-kilometer (118-mile) ride from Ceret at the foothills of the Pyrenees to the tiny mountain-bound nation of Andorra. “This was Sepp’s day,” said Jumbo-Visma teammate Wout van Aert, who helped put Kuss in a position to break. “He lives in Andorra and he was looking forward to …