The match was delayed for more than three hours by a torrential downpour with the first set tied at 3-3. Cuevas, who defeated Rafael Nadal in the semifinals, came out of the break fresher than Pella, a first-time ATP Tour finalist.
In the women's final, former French Open champion Francesca Schiavone defeated American Shelby Rogers 2-6, 6-2, 6-2 for her seventh WTA title. The victory marked a turnaround for the Italian, whose ranking has slipped to No. 132 after reaching No. 4 in 2011.
The Rio Open was plagued by rain all week and the men's final was played in a sparsely filled center-court stadium.