Spaniard Valverde moved 21 seconds clear of Froome in the general classification in the week-long race after leading the way in the 182km mountain stage from Valls to Lo Port along with Froome and compatriots Contador and Marc Soler.
He broke clear in the final 2km to finish 13 seconds ahead of Froome and Contador.
Valverde also won stage three at the top of La Molina on Wednesday, a day after he and his Movistar team mates were handed a one-minute penalty for illegal pushing during Tuesday's team time trial.
Valverde, who won the Tour of Catalonia and Tour of Spain in 2009, takes the leader's jersey from American Tejay van Garderen.
(Editing by Ed Osmond)
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