US Republican presidential hopeful Ted Cruz has won all 14 delegates in contention at a state party convention in Wyoming.
The delegates were chosen by party members rather than ordinary voters.
Donald Trump – who did not actively campaign in the state – remains the Republican front-runner overall.
However, the billionaire could fall short of the number of delegates needed to secure the Republican nomination for November presidential election.
That would mean a contested convention where voting for candidates starts again from scratch.
Mr Trump is concentrating on New York, which holds a key primary on Tuesday.
A number of senior Republican leaders have backed Mr Cruz, a Conservative Texas senator, fearing that Mr Trump’s controversial comments make him a weak candidate in the November election.
The result from the Wyoming contest brings Mr Cruz’s tally from 545 to 559 delegates. Mr Trump has 743.
In his victory speech on Saturday, Mr Cruz said: “If you don’t want to see Donald Trump as the nominee, if you don’t want to hand the general (election) to Hillary Clinton, which is what a Trump nomination does, then I ask you to please support the men and women on this slate.”
In the Democratic race, Ms Clinton is still ahead of her only remaining rival, Vermont Senator Bernie Sanders.