Belgium's Armee wins Vuelta 18th stage, Froome stays in red
The 31-year-old Armee (Lotto-Soudal) was the fastest among the breakaway of the 169-kilometer (105-mile) stage, finishing with a time of four hours, nine minutes and 39 seconds, ahead of Kazakh rider Alexey Lutsenko (Astana) and Italian Giovanni Visconti (Bahrain-Merida).
"That's fantastic. It's the best place to win a race," Armee said. "This is already my eighth year as a pro rider. I had to wait quite a long time to win a race."
Team Sky's Froome extended his lead in the general classification over Italian rider Vincenzo Nibali to 1 minute, 37 seconds, followed in third place by Dutchman Wilco Kelderman (Sunweb), who trails the red jersey by 2 minutes, 17 seconds.
Spaniard Sergio Pardilla (Caja Rural) was the fastest in a 20-man breakaway with 65 kilometers to go, a stretch that included four climbs.
The first one was Collada de Carmona, where Spain's Jose Joaquin Rojas (Movistar) led the breakaway to a 13-minute advantage over the peloton.
Heading to the climb of Collada de Ozalba, the title contenders started to attack and Spaniard Alberto Contador (Trek-Segafredo) got the better of then-leader Joaquim "Purito" Rodriguez on the Collada de la Hoz.
Armee and Lutsenko broke away on the fourth climb.
"I felt better and better during the stage and I just went full gas on the last climb," Armee said.
For Froome, the final climb provided a chance to gain time on his main rivals.
"Today worked out perfectly in my favor," Froome said. "It was a really tough stage, a lot of GC guys tried to attack on the penultimate climb."
"Once we got to that final climb, the team did a really strong pace at the bottom and I think some guys paid for their efforts from yesterday and their attacks earlier on today," he added.
Friday's 19th stage will run from Caso to Gijon for 149.7 kilometers.