On a day when Wout Poels celebrated in the Tour of Britain, Roche out-sprinted escape companion Haimar Zubeldia (Trek Factory Racing) for the 18th stage in Riaza northwest of Madrid.
The win also helped Sky stay at the top of the teams’ classification, a battle they are trying to win against team Movistar before the Vuelta pulls to a stop in Madrid on Sunday.
"I'm pretty sure already I'll have a message by now from Chris, we have a great relationship," Roche said after stepping off the podium with the winner's flowers.
"He's been very supportive, and I thanked him for letting me attack on the first day. It's been good to get a bit of freedom, and great to be able to make the most of it because don't get so many opportunities."
The 31-year-old joined from team Tinkoff-Saxo over the winter to help Froome. This spring, he was assigned to Richie Porte and helped him win races like Paris-Nice, and this summer, he turned his attention to Froome with wins in the Critérium du Dauphiné and of course, the Tour de France.
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Roche already had his opportunity in stage two, but after Froome left the Vuelta with a broken bone in his foot, the green light shined brighter.
It was not easy as Roche crashed twice in the race and scraped and bruised his right hip. It took him a four to five days to recover. He benefited from Tuesday's rest day and Wednesday, when Sky let him go easy in the time trial.
Watch: Vuelta a Espana essential guide
"We had a few days of misfortune. It was big blow losing Chris Froome, tough to lose our GC opportunity, and I was really struggling with my hip," Roche said.
"There was also good days: Mikel and Ian raced well, Ian Boswell placed [third] on a mountain stage.
“We've been very aggressive, and it's been good to see a more aggressive team Sky in the Vuelta. It's not the Vuelta everyone wanted, but not a bad Vuelta."
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