Mexico (3-2) will play Cuba's Pinar de Rio, who beat Venezuela's Caribes de Anzoategui in its semifinal on Saturday. The Dominican Republic, the host of the 2016 Caribbean Series, finished 2-3.
"This is a beautiful island, but we are not here on a vacation," said Mexico manager and former Major League infielder Benji Gil. "We didn't just come for the trip. We came to win."
Scoreless after the first inning, Mexico scored three runs in the top of the second, including two on an error by Dominican Republic third baseman Hector Gomez for an early 2-0 lead. D-backs infielder Walter Ibarra scored on a sacrifice fly to make it 3-0.
Former Major Leaguer Russell Branyan drove in a run in to push Mexico ahead, 4-0, in the third. Second baseman Jose Manuel Rodriguez scored another run for Mexico in the sixth.
Branyan finished 1-for-2 with one run scored and one RBI.
The Dominican Republic rallied for two runs in the sixth and Tampa Bay infielder Alexi Casilla scored in the eighth to cut Mexico's lead to 5-3. Houston Astros infielder Jonathan Villar came home on a ground ball by Robinson Diaz in the ninth inning to shrink Mexico's advantage to one run. Casilla grounded out to second base with the potential tying run on third to end the game.
"This was a game with a lot of drama," Gil said. "I congratulate the Dominican team, their manager and everybody from the Gigantes. I am very happy with my players and their effort. This was a tough game against a tremendous rival."
Mexico's Yaquis de Obregon won Caribbean Series titles in 2011 and '13. The Naranjeros de Hermosillo won the title last year on Margarita Island in Venezuela.
The Dominican Republic (1997-99) is the only country to win three consecutive Caribbean Series titles since 1970.
Jesse Sanchez is a national reporter for MLB.com. Follow him on Twitter @JesseSanchezMLB. This story was not subject to the approval of Major League Baseball or its clubs.