Tomasz Marczynski claimed his second stage win at the 2017 Vuelta a Espana as Chris Froome saw 20 seconds cut from his general classification lead after mechanical issues and falls.
Lotto Soudal rider Marczynski triumphed in stage six and was first across the line again at the end of the 160.1-kilometre ride from Motril to Antequera, which proved damaging to Froome's lead.
The red jersey wearer added 43 seconds to his advantage on Wednesday but lost almost half that as he had to change bike and hit the deck twice on the final descent.
Froome now sits 59 seconds ahead of Bahrain-Merida rider Vincenzo Nibali, who has taken huge strides in his GC challenge this week.
Marczynski was part of the breakaway during the flat section along the coast and he did not push clear until the last 4km of the category two climb up to Puerto del Torcal - the second ascent of the day.
No one was able to stay on the Pole's wheel and the gap grew as he comfortably navigated the descent to cross the line 52 seconds ahead of the chasing pack, with Omar Fraile (Dimension Data) taking second ahead of Jose Joaquin Rojas (Movistar).
Froome was sat in the peloton over nine minutes behind the leaders when he had to pull over and change bike, slipping on a tight bend in his haste to make up lost time.
Fellow Team Sky riders Wout Poels and Mikel Nieve dropped back to aid the Tour de France champion's push, which limited the damage done to his lead.
GOOD DAY/BAD DAY
Alberto Contador launched an attack on the second climb and managed to gain more than 40 seconds on Froome, despite being over a minute clear of the Team Sky rider when he suffered his fall.
The Spaniard is now just one minute behind Esteban Chaves in the final podium position, giving him cause to dig in before the race reaches its conclusion next weekend.
Aqua Blue Sport, competing in their first Grand Tour, discovered their team bus had been set on fire overnight in Almeria. No one was hurt in the incident and Peter Koning gave them cause for cheer by finishing the stage in 11th.
1. Tomasz Marczynski (Lotto-Soudal) 3:56:45
2. Omar Fraile (Dimension Data) +00:52
3. Jose Joaquin Rojas (Movistar) +00:52
4. Pawel Poljanski (Bora-Hansgrohe) +00:52
5. Stef Clement (Lotto NL-Jumbo) +00:52
1. Chris Froome (Team Sky) 49:22:53
2. Vincenzo Nibali (Bahrain-Merida) +00:59
3. Esteban Chaves (Orica-Scott) +02:13
1. Matteo Trentin (Quick-Step Floors) 78 pts
2. Chris Froome (Team Sky) 75 pts
3. Pawel Poljanski (Bora-Hansgrohe) 58 pts
KING OF THE MOUNTAINS
1. Davide Villella (Cannondale-Drapac) 38 pts
2. Jose Joaquin Rojas (Movistar) 27 pts
3. Chris Froome (Team Sky) 18pts
Stage 13 begins with a category three climb but is ultimately a flat stage, offering sprinters a final chance to make inroads before a gruelling run in the mountains.