Alessandro De Marchi (BMC Racing) claimed his first individual victory since the 2015 Vuelta a Espana, soloing away to win in Luintra over Katusha-Alpecin's Jhonathan Restrepo.
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The Italian's stage win was only part of the story, as Frenchman Thibaut Pinot (Groupama-FDJ) also made the move and put pressure on race leader Simon Yates (Mitchelton-Scott) when the breakaway's gap put him in the virtual lead by 90 seconds.
In the end, the group of favourites with Yates was pulled back thanks to help from Movistar, with Alejandro Valverde keeping his second place overall by one second, and Nairo Quintana remaining third at 14 seconds.
The overall classification remains locked up tight, with the top 10 separated by just 47 seconds heading into stage 12.