Ted Cruz, a fiery, conservative Texas senator loathed by his own party’s leaders, swept to victory in Iowa’s Republican caucuses, overcoming billionaire Donald Trump.
Among Democrats, Hillary Clinton and Bernie Sanders were deadlocked in a tight race.
Mr Cruz’s victory was a harsh blow to Mr Trump, the supremely confident real estate mogul who has rocked the Republican field for months with controversial statements about women and minorities.
The victory in the first Republican nominating contest ensures that Mr Cruz will be a force in the presidential race for weeks to come – if not longer.
The first-term Texas senator now heads to next week’s New Hampshire primary as an undisputed favourite of the furthest right voters, a position of strength for drawing in evangelical voters and others who prioritise an abrupt break with President Barack Obama’s policies.
Perhaps most importantly, his win denied Mr Trump a huge opportunity to gain momentum heading into New Hampshire.