Puerto holds a "winner-take-most" primary, meaning that some delegates may go to runners-up, depending on the final vote tally.
The win came after a miserable Saturday for Rubio. He placed third behind Trump and Sen. Ted Cruz (Tex.) in contests held in Kansas, Kentucky and Louisiana and fourth in Maine behind Trump, Cruz and Ohio Gov. John Kasich.
Trump still leads the pack with 382 delegates, while Cruz has 300 delegates, according to an AP tally. Rubio will have 151 delegates if he wins every available slot in Puerto Rico. At least 1,237 delegates are needed o secure the Republican presidential nomination.
In Puerto Rico on Saturday, Rubio campaigned in Toa Baja and brought along some star power: Actor Carlos Ponce, his former brother-in-law, called the senator "a man of deep faith who is going to be an excellent representative and president," according to local news reports.
Idaho and Michigan will hold primaries on Tuesday. Rubio was campaigning in Idaho on Sunday and plans to visit the Tampa and Orlando areas on Monday as he begins his bid to win the winner-take-all Florida GOP Primary on March 15.
Puerto Rico is a U.S. commonwealth that has only nonvoting representation in Congress and uses different political parties than Democrats and Republicans to run island affairs. Puerto Ricans may participate in the Democratic and Republican primaries, but they cannot vote in November's presidential election. But residents who move to the mainland United States are eligible to vote in the presidential election.
Millions of Puerto Ricans have fled the island in recent years amid its deteriorating economic situation -- and most have relocated to Rubio's native Florida. The exodus has been sparked in part by a $72 billion debt that Congress, the Treasury and bondholders are grappling with how to address and that has crippled the local economy. A growing number of Zika virus cases also are likely to affect tourism, a vital source of revenue on an island with 3.5 million residents.
Puerto Rican leaders are seeking Chapter 9 bankruptcy protection, but federal law bars the commonwealth from doing so. The Obama administration and Congress seem to have moved away from legislation that would allow leaders to file for such protection, but leaders continue pushing for such changes to avoid a drawn-out debt restructuring.
Rubio has declined to support Chapter 9 protection.
“This year alone, with all the problems they’re having, they barely cut their budget from one year to the next,” he said recently when asked about such protection. “So, I think the leadership on the island has to show their willingness to get their house in order and put in place measures [to] allow the economy there to grow again.”
Rubio added that “the leaders in charge there now are doing a terrible job.”
Steven Mufson contributed to this report.