He did so by finishing ahead of Alberto Contador, his Spanish compatriot and nearest challenger for the leader's red jersey.
Contador had tried to escape late on in the 149.2km ride from Palas de Rei to Puerto de Ancares but Rodriguez (Katusha) responded to the threat before sprinting clear to claim his third stage win of the 2012 Vuelta in a time of four hours, 10 minutes and 28 seconds.
Contador (Saxo Bank-Tinkoff Bank) was five seconds behind while their countryman Alejandro Valverde (Movistar) was third, 13 seconds adrift of the winner.
Chris Froome of Team Sky came home fifth, 38 seconds behind Rodriguez.
Saturday's results mean that Rodriguez extends his lead over Contador at the top of the leaderboard to 22 seconds, while there is now a gap of one minute, 41 seconds to the next-best riders, who are Briton Froome and Valverde.