Shortstop Ivan De Jesus Jr., who played in 104 games for the Reds last season and signed a Minor League deal with the Brewers last December, scored on Castillo's first-inning home run. De Jesus finished the game with three hits in Puerto Rico's first victory of the tournament.
The loss drops the Dominican Republic to 0-3.
As for Castillo, his story is well-known. He signed a seven-year, $72.5 million deal with the Red Sox in 2014 and hit .333 with one double, two home runs, six RBIs in 10 games that season. He hit .253 with 10 doubles, two triples, five home runs, and 29 RBIs in 80 games for the Red Sox the next year and spent most of 2016 in Triple-A. He appeared in nine games and had eight at-bats in the big leagues last season.
Castillo has played winter ball in Puerto Rico since he signed with the Red Sox to stay sharp heading into Spring Training.
"My expectations, first is to stay in the big leagues," Castillo said. "I have set that goal for this year. And to just keep showing support to the Boston team. Those are the goals and I hope to see those results."
Castillo is blocked in the big leagues by outfielders Mookie Betts, Jackie Bradley Jr., and Andrew Benintendi. Veteran outfielder Chris Young will be used off the bench. The Red Sox can also avoid exceeding the luxury-tax threshold by keeping Castillo off the 40-man.
"I just think on what I have to do and that is playing baseball," Castillo said. "I do not focus on what Boston does with me. I just focus on playing baseball."
De Jesus Jr. had three more hits on Saturday to up his hit total to nine in 13 at-bats. He's hit one home and driven in four runs. He also has one double and has walked three times.
Play of the game
Puerto Rico collected 11 hits in the game, including three hits each by De Jesus, Castillo and third baseman David Vidal, but it was Castillo's home run that set the tone.
Phillies shortstop Freddy Galvis had three hits and drove in two runs to help lead Venezuela to an 8-3 victory against Cuba in the nightcap at Estadio Tomateros.
The victory guarantees a spot in Monday's semifinal games for Venezuela (2-1) and will prevent the Dominican Republic (0-3) from advancing to the next round with Mexico (3-0) and Cuba (2-1).
Venezuela scored three times in the first inning, two on an RBI single by Jose Castillo that scored Galvis, who finished 3-for-4 with two runs scored, and former Major League infielder Ronny Cedeno for an early lead.
Cuba answered in the top of the second with a three-run home run by Carlos Benitez to tie the game at 3, but Cedeno stung Venezuela again, this time with an RBI single that scored Galvis to push Venezuela ahead, 4-3, in the fourth. Second baseman Ali Castillo, who split last season between Double-A and Triple-A for the San Francisco Giants, drove in a run in the bottom of the fifth to give Venezuela a two-run lead.
Galvis' two-run double put his team up 7-3 and put the game away.
The Galvis and Cedeno combination at the top of the lineup proved to be too much for Cuba. The duo combined to go 6-for-9 with three runs and three RBIs.
Play of the game
Cedeno's fourth-inning RBI gave Venezuela a lead and it never looked back. Cedeno played parts of 10 seasons with the Cubs, Mariners, Pirates, Mets, Astros, Padres and Phillies.