Mendoza held Puerto Rico hitless through seven, before a leadoff double in the bottom of the eighth, and finished hurling 7 1/3 shutout innings, leading Mexico's Yaquis de Obregon to a 10-0 thrashing on Wednesday and setting up a matchup against the Dominican Republic's Leones del Escogido in the final.
Thursday's championship, the first of its kind in a Caribbean Series that used to be strictly double round robin, will take place at 7 p.m. MT, in front of an Estadio Sonora crowd desperate to see Mexico win a title while hosting the Caribbean Series for the first time since '05.
Mexican Rodrigo Lopez, who pitched 11 years in the Majors, will face off against Dominican Angel Castro.
"This is for the team," Mendoza said in Spanish. "We're one team, and everyone deserves this victory."
Obregon, the champion in 2011 and making its third straight trip to the Caribbean Series, is 3-3 and needed the win over Puerto Rico's Criollos de Caguas (2-4) to secure a trip to the final.
Escogido, searching for its second straight title and third in four years, is 5-1 and clinched a spot in the title with an 11-6 win over Obregon on Tuesday. Earlier on Wednesday, it beat Venezuela's Navegantes de Magallanes, 4-2, thanks to a go-ahead two-run homer by first baseman Francisco Pena in the top of the ninth.
Venezuela, whose last Caribbean Series title came in '09, finished 2-4.
One start removed from tossing six shutout innings, Mendoza gave up two hits on four walks and nine strikeouts in an outing that saw him expend 113 pitches. Heading into the eighth, he had retired 10 of his last 11 batters, five via strikeout. But Daniel Ortiz led off with a double to right-center field.
Then, after seeing Mendoza allow a one-out single to Jesus Feliciano, Obregon manager Eddie Diaz removed the 29-year-old right-hander, who got a standing ovation from a raucous sold-out crowd.
"I'm going to try to take this into Spring Training," said Mendoza, who will likely end up as the Royals' long reliever. "That and my health is most important. I finished strong and I felt good throughout, and that was the best part of this."