US Senator Marco Rubio, who has fallen behind frontrunner Donald Trump and rival Ted Cruz in the race for the Republican presidential nomination, scored a victory Sunday in the conservative party's primary vote in Puerto Rico.
With about half of the vote counted, he had more than 70 per cent, and US television networks projected him to win easily.
Rubio, who is Cuban-American and represents Florida in the Senate, was on pace to win more than 50 per cent of the vote on the island, a US territory in the Caribbean. An outright majority would give him all 23 of Puerto Rico's delegates to the Republican nominating convention in July.
Trump was in second place with 12 per cent.
Puerto Rico is not a state and has no voice in the November presidential elections, but both the Republicans and the left-leaning Democratic Party award the state convention delegates.