Rivas, who was recalled Friday from Triple-A Iowa, capped Chicago's eight-run second with a three-run homer. He tacked on RBI singles in the fourth and fifth.
The Cubs finished with 23 hits in their most lopsided shutout win dating to at least 1901.
Nico Hoerner collected a career-high four hits, and Seiya Suzuki, Willson Contreras and Ian Happ had three hits apiece. It was more than enough support for Kyle Hendricks, who pitched seven innings of two-hit ball.