Nikki Haley has defeated Donald Trump in the Republican primary in Washington DC, BBC reports.
This is her first victory over the former president in the 2024 campaign to become the Republican presidential candidate.
She lost in South Carolina, her home state. But she is the first woman to win a Republican primary in US history.
Mr Trump however has a huge lead over Ms Haley and is likely to face Joe Biden in the November election.
The BBC's US partner CBS reports that Ms Haley will receive all 19 Republican delegates who were up for grabs in Washington DC, giving her 43 delegates nationwide - well behind Mr Trump's 247.
Ms Haley, a former US ambassador to the UN, won 62.9% of the vote, to Mr Trump's 33.2%.
It is seen as a largely symbolic win, as the capital is a heavily Democrat-leaning jurisdiction, with only about 23,000 registered Republicans in the city.
Local party officials said 2,035 Republicans participated in the primary, the Washington Post reported.
Ms Haley's campaign national spokesperson Olivia Perez-Cubas said: "It's not surprising that Republicans closest to Washington dysfunction are rejecting Donald Trump and all his chaos".
The Trump Campaign, however, was quick to dismiss Ms Haley's win, calling her the "Queen of the Swamp".
"While Nikki has been soundly rejected throughout the rest of America, she was just crowned Queen of the Swamp by the lobbyists and DC insiders that want to protect the failed status quo. The swamp has claimed their queen," Trump Campaign press secretary, Karoline Leavitt, said.
Mr Trump has dominated every state primary or caucus so far in the Republican campaign, and is poised to win more delegates this week, on Super Tuesday, when voters in 15 states and one US territory will nominate their candidate. It is the biggest day of nominating contests, with 874 Republican delegates' support at stake.
Ms Haley has vowed to stay in the race until at least 5 March, when thousands of people in will cast their votes on Super Tuesday.
