The third-ranked Radwanska started the day by beating Maria-Teresa Torro-Flor 6-3, 6-2 for her second singles victory of the series, only for sister Urszula Radwanska to lose to Silvia Soler-Espinosa 6-1, 6-3 on the outdoor red clay at Barcelona's Olimpico Estadio.
That left the series level at 2-2 and set up the doubles match where Agnieszka Radwanska and Rosolska beat Soler-Espinosa and Anabel Garrigues 6-4, 6-2.
The Polish pair were a break down at 4-3 in the first set, but they responded by winning seven straight games to claim the first set and build a commanding 4-0 lead in the second.
"We're Polish, we're tough, so we're not giving up any points," Radwanska said.
Earlier, Radwanska broke Torro-Flor seven times to win her second singles match in two days.
Spain captain Conchita Martinez, a former Wimbledon winner, praised Radwanska.
"She can do pretty much everything that she wants to do," Martinez said. "She can serve pretty good, she can volley, she can drop shot, she can run, but what I like the most is that she's one of the most consistent, or the most consistent player, on the tour. She always wins the matches that she has to."
In the second reverse singles match, Soler-Espinosa hit seven aces and 27 winners to deal Urszula Radwanska her second loss in the series.