American rider Sepp Kuss won the mountainous 15th stage of the Spanish Vuelta, while Jumbo-Visma teammate Primoz Roglic withstood a sustained attack by Alejandro Valverde to keep the overall race lead on Sunday.
Kuss pulled clear of a small breakaway group on the final of four climbs to claim the grueling 154.4-kilometer (96-mile) stage from Tineo to a summit finish at Santuario del Acebo in 4 hours, 19 minutes.
"It's pretty big I guess. Honestly it hasn't quite sunk in," Kuss said. "It is an incredible day."
World champion Valverde launched his attack midway up the last category-one climb and Roglic stuck to his wheel, while the other top riders fell behind. Roglic finished right in front of Valverde, the 2009 Vuelta winner.
Roglic, a Slovenian ex-ski jumper who is aiming for his first Grand Tour victory, leads Valverde by 2 minutes, 25 seconds.
With one week of racing left, the Vuelta looks like Roglic's to lose. He took the leader's red jersey with a dominant performance on the time trial during Stage 10. Only Valverde, who at age 39 is 10 years Roglic's senior, has been able to match his power and consistency in the mountains.
Tadej Pogacar lost time and is third overall at 3:42 back. Miguel Ángel López fell to 3:59 back, and Nairo Quintana lost even more time to sit 5:09 off the pace.
Kuss, who won the Tour of Utah last year, crossed 39 seconds ahead of stage runner-up Ruben Guerreiro. The 24-year-old Kuss celebrated by giving high fives with fans lining the barriers before the finish line.
"I think that is what makes the Vuelta so special, the passion of the fans," Kuss said. "I have good days when you feel their enthusiasm, but on the bad days when you're 30 minutes behind the winner, they are there to cheer you and give you a push, that is what makes cycling special."
Monday's stage is another tough trek in the green northern mountains, taking riders more than 144 kilometers (89 miles) from Pravia to a beyond-category summit finish atop the Alto de la Cubilla.
The three-week race ends in Madrid on Sept. 15.