Tomasz Marczynski took the honours on stage six of La Vuelta as overall leader Chris Froome saw nearest challenger Tejay van Garderen slip down the standings.
Lotto Soudal rider Marczynski, who had never claimed a stage win in a Grand Tour event, pipped fellow Pole Pawel Poljanski (Bora-Hansgrohe) and Spaniard Enric Mas (Quick-Step Floors) to the line following a sprint finish on the streets of Sagunto.
The trio finished the 204.4-kilometre stage from Vila-Real in a time of four hours, 47 minutes and two seconds, with the pairing of Leon Luis Sanchez (Astana) and Jan Polanc (UAE Team Emirates) completing the top five as they crossed the line eight seconds later.
"I came here very motivated, I thought I could achieve something and today was the day," said Marczynski after the biggest win of his career.
"It was a very tough stage, a big breakaway. We went up the last climb very quickly.
"I said I was going to give it my all and it went perfectly."
Overall leader Froome, meanwhile, was part of an 18-strong body of riders that finished next, 26 seconds back. That group included many of Froome's biggest rivals at the top of the classification - but not Van Garderen.
The American started the day 10 seconds behind Froome in second place overall, but the BMC Racing rider crashed twice in the closing stages on Thursday and he now lies 30 seconds adrift of the leader in fourth place.
That means Froome's lead at the top of the standings increases marginally to 11 seconds - the gap to Colombian Esteban Chaves of Orica-Scott - as he stays on course to become just the third man to win the Vuelta and Tour de France in the same year
Ireland's Nicolas Roche (BMC) moves up a place to third ahead of Van Garderen, remaining 13 seconds behind the red jersey.
Italy's Vincenzo Nibali, one of only six riders in history to have won the Vuelta, Tour de France and Giro d'Italia during their careers, is 36 seconds back in fifth spot after clocking the same time as Froome on Thursday.
Friday's seventh stage contains another three categorised climbs on the 207km from Lliria to Cuenca.
Stage Six result (Villarreal - Sagunt, 204.4 km)
1. Tomasz Marczynski (Poland / Lotto-Soudal) 4:47:02"
2. Pawel Poljanski (Poland / BORA-hansgrohe) ST
3. Enric Mas (Spain / Quick-Step Floors)
4. Luis Leon Sanchez (Spain / Astana Pro Team) +8"
5. Jan Polanc (Slovenia / UAE Team Emirates)
6. Warren Barguil (France / Team Sunweb) +26"
7. Giovanni Visconti (Italy / Bahrain-Merida)
8. Chris Froome (Britain / Team Sky)
9. Fabio Aru (Italy / Astana Pro Team)
10. Jack Haig (Australia / Orica-Scott)
General classification (after Stage Six)
1. Chris Froome (Britain/Team Sky) 22:54:38"
2. Esteban Chaves (Colombia/Orica-Scott) +11"
3. Nicolas Roche (Ireland/BMC Racing Team) +13"
4. Tejay van Garderen (US/BMC Racing Team) +30"
5. Vincenzo Nibali (Italy/Bahrain-Merida) +36"
6. David De La Cruz (Spain/Quick-Step Floors) +40"
7. Fabio Aru (Italy/Astana Pro Team) +49"
8. Adam Yates (Britain/Orica-Scott) +50"
9. Michael Woods (Canada/Cannondale-Drapac) +1:13"
10. Simon Yates (Britain/Orica-Scott) +1:26"