Chris Froome (Team Sky) battled gallantly to ensure he lost no more time on race leader Nairo Quintana (Movistar) on another tough day at the Vuelta a España.
Mathias Frank took IAM Cycling's second win of the race from the breakaway on the stage which finished with a brutal climb to Penygolosa, but the key battle was being waged four minutes behind in the peloton.
Quintana looked to have ridden himself of Froome once and for all as he escaped on the climb with Alberto Contador (Tinkoff) and Esteban Chaves (Orica-BikeExchange) but the Brit plugged away to stay in contention.
The day's 28-man breakaway included two men each from Sky and Movistar, including Leopold Konig, who was flying high in the GC until Sunday's decisive stage 15.
Frank and Dario Cataldo (Astana) played their cards early, breaking from the large escape in the final 20km, opening up a 30 second lead by the bottom of the climb.
Robert Gesink (LottoNL-Jumbo) upped the pace as the breakaway hit the steep inclines of the final ascent, with Frank and Cataldo maintaining a small lead in the lower slopes.
Four minutes back down the road, Movistar flocked to the front of the diminished bunch on the narrow roads to keep Quintana safe as they hit the bottom of the climb.
Gesink continued to set the pace behind Frank and Cataldo, ignoring the couple of attacks made by the likes of Pello Bilbao (Caja Rural) and Kristian Sbaragli (Dimension Data) and maintaining his own pace.
Frank left Cataldo behind and Gesink reeled the Italian in as well as Konig (Team Sky) and José Herrada (Movistar) also crawled back into contention.
In the peloton, Movistar swamped the front, leaving little room for any attacks, but Contador squeezed through onto the open road ahead of the bunch.
As Frank crossed the line, Quintana moved up to join Contador and Chaves. Froome was slow to react but clawed his way back to the elite group.
Chaves then upped the pace, leaving Froome struggling to keep up once more. Froome's high cadence ensured he made up the ground on the trio and even edged past Quintana on the line to keep his slim chances of overall victory alive.
Stage 18 could provide an opportunity for the sprinters, with a rolling run to Gandia, although the GC contenders are running out of time to gain back time.
Vuelta a España stage 17, Castellon - Penygolosa (177km)
1. Mathias Frank (Sui) IAM Cycling, 4-34-38
2. Leopold Konig (Cze) Team Sky, at 6s
3. Robert Gesink (Ned) LottoNL-Jumbo, at 11s
4. Pello Bilbao (Esp) Caja Rural, at 14s
5. Dario Cataldo (Ita) Astana, at 16s
6. José Herada (Esp) Movistar, at 29s
7. Axel Domont (Fra) Ag2r La Mondiale, at 48s
8. Bart de Clercq (Bel) Lotto-Soudal, at 57s
9. Kristijan Durasek (Cro) Lampre-Merida, at 1-02
10. Haimar Zubeldia (Esp) Trek-Segafredo, at 1-04
Overall standings after stage 17
1. Nairo Quintana (Col) Movistar, 69-35-32
2. Chris Froome (GBr) Team Sky at 3-37
3. Esteban Chaves (Col) Orica-BikeExchange at 3-57
4. Alberto Contador (Esp) Tinkoff at 4-02
5. Simon Yates (GBr) Orica-BikeExchange at 6-03
6. Andrew Talansky (USA) Cannondale-Drapac at 7-34
7. Samuel Sanchez (Esp) BMC Racing at 8-12
8. Davide Formolo (Ita) Cannondale-Drapac at 8-13
9. Michele Scarponi (Ita) Astana at 8-28
10. David de la Cruz (Esp) Etixx-Quick Step at 8-52
