Jon Magunazelaia grabbed the crucial try, while Deccie Cusack added eight points as Gernika, famed by Pablo Picasso, made a real impression as European rugby continues to develop.
Cusack, who joined the Basque club from Munster in the summer, was thrilled with the significant victory.
"It showed we have learned from the first two games," said the fly-half.
"To see his delight of the older players after Saturday's game was something else. The other players who played with the team for five or six years and are from the village of Gernika, everyone was over the moon.
"There was a buzz around the street. "
Rovigo are yet to win in this season's competition and sit bottom of Pool Four following their latest defeat.
They have lost 48 out of their 51 matches in the European club competition but they will be hoping to gain revenge at Stadio Mario Battaglini.
• Rovigo have lost their last 25 Amlin Challenge Cup matches in succession.
• After conceding an average of 87.5 points in their opening two fixtures, Gernika managed to stop Rovigo from scoring any tries in their 13-3 victory over the Italian side last week.
• Between them, only five different players have scored points for these two teams this season.