Discussions followed in the GC group, but with Contador on the march – and now linked up with team-mate Theuns – there was no time for them to wait for the race leader.
Astana in particular pushed on, despite the hesitation, but Team Sky did superbly to limit the damage – riding in sight of the front group as the line approached.
Contador held a minute’s advantage at its peak, meanwhile, but faded in the final kilometres when he had to go it alone, ultimately finishing 22 seconds clear of GC group.
Froome lost 20 seconds, but remains the race leader with just less than a minute’s lead over Vincenzo Nibali.
Vuelta a Espana 2017: stage 12 – result
1) Tomasz Marczynski (POL) – Lotto-Soudal – 3.56.45hrs
2) Omar Fraile (ESP) – Dimension Data +52”
3) Jose Joaquin Rojas (ESP) – Movistar – ST
4) Pawel Poljanski (POL) – Bora-hansgrohe
5) Stef Clement (NED) – LottoNL-Jumbo
6) Brendan Canty (AUS) – Cannondale-Drapac +1.42
7) Anthony Perez (FRA) – Cofidis +2.50
8) Jan Polanc (SVN) – UAE Team Emirates – ST
9) Andreas Schillinger (GER) -Bora-hansgrohe
10) David Arroyo (ESP) – Caja Rural-Seguros +3.00
General classification
1) Chris Froome (GBR) – Team Sky – 49.22.53hrs
2) Vincenzo Nibali (ITA) – Bahrain-Merida +59”
3) Johan Esteban Chaves (COL) – Orica-Scott +2.13
4) David de la Cruz (ESP) – QuickStep Floors +2.16
5) Wilco Kelderman (NED) – Team Sunweb +2.17
6) Ilnur Zakarin (RUS) – Katusha-Alpecin +2.18
7) Fabio Aru (ITA) – Astana +2.37
8) Michael Woods (CAN) – Cannondale-Drapac +2.41
9) Alberto Contador (ESP) – Trek-Segafredo +3.13
10) Miguel Angel Lopez (COL) – Astana +3.51