Puerto Rico awarded delegates proportionally. However, there was a trigger that awarded all 20 delegates to a candidate who won more than 50 percent of the vote, and Romney was on pace to finish well above the threshold.
Romney leads the overall race for delegates, with 521, including endorsements from Republican National Committee members who automatically attend the convention and can support any candidate they choose.
Former Pennsylvania Sen. Rick Santorum has 253 delegates, former House Speaker Newt Gingrich has 136 and Texas Rep. Ron Paul has 50.
It will take 1,144 delegates to win the Republican nomination for president at the party's national convention in August.
So far, Romney has won 53 percent of the primary and caucus delegates, putting him on pace to clinch the nomination in June
-- but not leaving much room for error.
Santorum has won 27 percent of the delegates and Gingrich has won 14 percent. At this rate, their only hope is to prevent Romney from reaching 1,144 delegates, and waging a floor fight at the party's convention in Tampa, Fla.
Next up: The Illinois Republican presidential primary on Tuesday, with 54 delegates up for grabs. Santorum, however, will only be eligible to win 44 delegates because his campaign did not file a full slate of delegates.