Rubio spokesman Alex Conant quickly tweeted that Rubio's victory showed that the Florida senator can be a unifier.
"DC's changed a lot in last decade. It's a minority-majority city that's embracing the future. And today voted for it," Conant tweeted.
Rubio picked up 10 delegates in the vote, and John Kasich picked up 9.
The results came soon after Texas Sen. Ted Cruz picked up nine of the 12 delegates awarded in Wyoming's county conventions. GOP front-runner Donald Trump gained one delegate, as did Rubio. One delegate is uncommitted.
The other 14 delegates will be elected April 16 at the state convention.
Earlier Saturday, Hillary Clinton won the first-ever Northern Mariana Islands Democratic caucuses, according to final results from the local Democratic Party. Cruz, meanwhile, picked up a delegate in Guam, but the territory's other five delegates remain uncommitted.
In the Northern Mariana Islands, Clinton received 102 total votes (54%), compared to 65 votes for Bernie Sanders (34%). An additional 22 votes were cast for "uncommitted."
The former secretary of state picked up four additional delegates with her win, while Sanders earned two delegates. Clinton already had the support of an unpledged superdelegate from the Northern Marianas.
This is Clinton's 14th victory in her quest for the Democratic presidential nomination and her second in a U.S. territory. She won the American Samoa caucus on Super Tuesday, March 1. Bernie Sanders has won nine contests, most recently his upset victory over Clinton in Michigan on March 8.
Voting was held Saturday evening on the islands Tinian, Saipan and Rota. It was the only Democratic contest held this weekend.
Big turnout in D.C.
In Washington, thousands showed up during the day to both vote for their choice for the GOP nominee as well as delegates to this summer's convention in Cleveland. Mid-afternoon, during a light rain, hundreds of D.C. Republican voters were standing in a line which stretched for three city blocks -- and had been for several hours -- as they waited to get inside to vote.
Some people waited in line for two hours to get inside.
"It's a pretty exciting thing, here in Washington, D.C.," Patrick Mara, executive director of the DC Republican Party, told CNN. "These are very dedicated, devoted Republicans."
Some of those waiting in line said they showed up because this was a unique opportunity.
"We know that there are not that many Republicans in the city, so we're happy everyone came out," District resident Peggy Ehrhardt told CNN.
Some supporters of Trump and John Kasich were on hand hoping to sway those waiting in line to support their candidate. There was also a woman handing out anti-Trump stickers to the folks waiting.
Another woman waiting to vote told CNN, "This is pretty remarkable ... I'm in line because this is a one chance where a Republican vote in D.C. counts."
Guam still mostly uncommitted
Also Saturday, Cruz picked up a delegate from the faraway territory of Guam, but the big winner on the island this weekend was "uncommitted."
Guam's Republican Party met early Saturday morning -- Friday evening in Eastern Time -- to elect delegates to this summer's convention in Cleveland. Six delegates were elected, but only one of them, Guam Gov. Eddie Calvo, has publicly endorsed a presidential candidate: Ted Cruz, according to party Executive Director Juan Carlos Benitez.
Benitez, himself a delegate, remains uncommitted, as do the other four elected delegates.
Benitez said the entire Guam delegation, the six delegates elected Saturday as well as the party chairman and the territory's two RNC reps, who all serve as automatic convention delegates, will meet within the next two weeks to hear from the four presidential campaigns and announce their endorsements.
Guam does not hold a traditional primary or caucus, in which candidates win delegates based on a presidential preference vote. Instead, delegates are elected directly at a party convention, and those elected delegates are free to support whomever they choose. Both the Republican and Democratic parties allow Guam and the other U.S. territories to participate in the presidential nomination process, although territories may not vote in the general election.
Guam Republicans met at the Dusit Thani Guam Resort in Tumon, where they heard phone calls, videos and letters from the four remaining candidates.
Cruz sent a letter that said in part, "It's Guam's time. ... Guam is of great strategic importance to the United States. It is time we treat it as such." Rubio sent a videotape calling for a new generation of leaders, and John Kasich made a live phone call in which he discussed veteran's health benefits and the Veterans Administration.
Trump described his call in a tweet late Friday night: "I just got off the phone with the great people of Guam! Thank you for your support! #VoteTrump today!"