Contador, a three-time Vuelta winner, attacked with around 20 kilometres to race. Once Froome crashed, his main rivals gained time with Nibali and his Bahrain-Merida team pushing the pace to reach Contador.
"The time I gained was due to as crash so it's too bad and Sky was already working hard," Nibali said. "So this time gain was not because I dropped them. Froome is still Froome."
Froome still the leader, but Contador gained 42 seconds and Nibali's group took 20. Froome now leads the race with 59 seconds on Nibali and 2-13 minutes on Esteban Chaves (Orica-Scott).
"I thought maybe that something would happen today but not like this. When Alberto Contador went, we were going completely all out to chase him. When Froome crashed, we were already going all out to retake Contador so there was no waiting," Nibali continued.
Alberto Contador attacks solo on stage 12 of the 2017 Vuelta a España (Sunada)
(Image credit: Yuzuru Sunada)
"In the moment that Froome crashed, Alberto began to gain a huge advantage and he's is always dangerous. This is Alberto's style. We know that. Today he showed that he's going really well."
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Contador remains in ninth place, but closed in on those ahead of him in the top-10.
He reached his team-mate Edward Theuns, who was riding in the escape that produced stage winner Tomasz Marczynski (Lotto-Soudal).
Theuns waited for around three minutes on the Puerto del Torcal climb for Contador to join and went to work afterwards on the downhill to the finish to Antequera, just inland from Malaga. Contador then pushed solo to the line.
He crossed at 7-25 minutes down, Nibali's group at 7-47 and Froome, who had the help of Wout Poels and Mikel Nieve, at 8-07.
"With a finish like that, that sort of time gap is about the best you can expect," Contador said.
"I attacked with Nicolas Roche, but he was in trouble following me, then I knew I had a team-mate ahead and gave it everything. I went as quickly as I could but was careful because knew the road could be slippery.
"Froome? I knew he fell, but he got up quickly, he's lost very little, tomorrow is a flat stage, and sure, he'll be good from here on."
On Friday, the race covers one of its rare flat days to Tomares. On Saturday, it climbs again for one of its nine summit finishes to Sierra de La Pandera.
"I knew people's legs would hurt a lot after the wet day yesterday," added Contador. "We gained some time, but let's take this on day by day. No stress."
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Gregor Brown is an experienced cycling journalist, based in Florence, Italy. He has covered races all over the world for over a decade - following the Giro, Tour de France, and every major race since 2006. His love of cycling began with freestyle and BMX, before the 1998 Tour de France led him to a deep appreciation of the road racing season.
