Florida Sen. Marco Rubio won Puerto Rico's Republican primary on Sunday, his second win of the race for the GOP presidential nomination.
Sen. Bernie Sanders, meanwhile, won the Democratic presidential caucuses in Maine.
The U.S. territory's three super-delegates have committed to Rubio.
Because he claimed a majority in Puerto Rico, he earns all 23 delegates from the island. That's an important boost for him after a disappointing slate of primaries on Super Tuesday.
In addition, officials say the votes that about 6,000 inmates cast on Friday won't be available until Wednesday.
Rubio also won Minnesota.
But he says his landslide win in Puerto Rico's primary is proof that he can expand his party in a general election.
The Florida senator is playing up his "electability" as he tries to catch GOP delegate leader Donald Trump and second-place Ted Cruz.
Rubio said in an interview Sunday that he "campaigned in Puerto Rico as a conservative" and still garnered more than 70 percent of the vote in an "open primary."
He said that "is evidence I can take conservatism to people who don't normally vote Republican" and win their support.
In Maine, Sanders defeated Democratic rival Hillary Clinton for his eighth win in the nomination process.
The win gave him more delegates than Clinton for the night. But it won't have much impact on Clinton's substantial lead overall.
With 25 Maine delegates at stake, Sanders is assured of winning at least 14 while Clinton stands to gain at least six.
He can now lay claim to winning eight of the 19 states that voted in primaries or caucuses to date, having also prevailed in Kansas and Nebraska over the weekend.
But Sanders is making little headway in delegates after Clinton's large margin of victory in Louisiana on Saturday.
Prior to the contest in Maine, Clinton had at least 1,123 delegates to Sanders' 484, including superdelegates - members of Congress, governors and party officials who can support the candidate of their choice.
It takes 2,383 delegates to win the Democratic nomination.
Cruz won in Maine's Republican caucuses on Saturday.
The fourth candidate on the GOP side, Ohio Gov. John Kasich, said over the weekend that he believes he can convince some of Trump's supporters to back him instead of the billionaire because he has better answers on how to fix the nation's problems.
He said he doesn't think it will be very hard to bring Trump voters his way as his message becomes more familiar. On the trail, Kasich often says he understands people's economic anxieties because he grew up in a scrappy blue-collar town in Pennsylvania.
"If they can hear me, and what I've done, that's the ticket. I believe that if I can sit with some Trump people - I won't get them all - if I can sit with them they're gonna understand that I'm one of them."
Meanwhile, Mitt Romney and other Republican establishment figures pressed ahead Sunday with their campaign to block Trump from capturing the party's presidential nomination, casting him as a shady businessman who rips people off with questionable enterprises such as the defunct Trump University.
"I want to make sure that the American people are not subject to the same kind of scam as we nominate a president," Romney told NBC's Meet the Press.
This article contains information from the Los Angeles Times.