Ireland's Nicolas Roche, who topped the general classifications earlier in the week, and Rigoberto Uran, were two high-profile casualties of the pile-up in the peloton at the 105-kilometre mark.
Uran's Education First teammate Hugh Carthy and home hope Victor de la Parte were also forced to retire.
Herrada and Teuns fought out the finish at Ares del Maestrat, the Valencian village perched 1,195m above sea level, at the conclusion of the 199km ride from Mora de Rubielos.
Teuns prised the red jersey from Miguel Angel Lopez, the Colombian who was unable to keep tabs with the stage's main protagonists and dropped to third overall.
Herrada's fellow Spaniard David de la Cruz moved up to second in the overall standings with a trio of title contenders Primoz Roglic, Nairo Quintana and Alejandro Valverde all still well-placed.
Teuns, who won a key stage in this year's Tour de France, was showing no ill effects from a freak accident at the start of the month.
The 27-year-old required 15 stitches after hitting his forehead on the steering wheel of a tractor while gardening at his home in Halen, forcing him to miss the San Sebastian Classic.
Herrada and Teuns were part of an 11-man breakaway at the 46km point, before surging clear in the closing stages to battle out the stage together.
Friday's mountainous seventh stage is a 183.2km ride from Onda to a summit finish at Mas de la Costa.