Hillary Clinton and Barack Obama battled to an impasse in their coast-to-coast Super Tuesday showdown, setting the stage for a protracted struggle for the Democratic nomination.
Senator Hillary Clinton won the key state of California, which is seen as a major victory for her campaign.
She also won in her home state of New York, as well as Arizona, New Jersey, Oklahoma and Tennessee, and took Massachusetts despite the endorsement of Barack Obama by the state's senior senator, Edward Kennedy.
In Arkansas she had an unsurprising win where she was first lady and the state she called home for 17 years.
In total she won eight states, with Senator Barack Obama winning 13.
Mr Obama won in Alabama, Alaska, Colorado, Connecticut, Delaware, Georgia, Idaho, Illinois, Kansas, Minnesota, Missouri, North Dakota, and Utah.
The Missouri win gives him the lion's share of the 72 delegates at stake in that state.
Mr Obama also got the majority of the 153 delegates in Illinois where he had been expected to easily beat Hillary Clinton in the state which he represents in the US Senate.
He surged to victory in Georgia, a state with a big bloc of black voters who have been his strongest supporters.
But the California Democratic primary was the biggest contest of the day and boosts Mrs Clinton's claim to the party's presidential nomination, while her win in New York gave her a huge share of the 232 delegates in that state. In bordering New Jersey she won a majority of 107 delegates up for grabs.
Supporters at her campaign headquarters in Manhattan cheered and waved placards as she took the stage with her husband, former president Bill Clinton, and daughter Chelsea.
'After seven years of a president who listens only to the special interests, you're ready for a president who brings your voice, your values and your dreams to your White House,' she said.
More than half the total delegates to the Democratic party convention in August were up for grabs on Super Tuesday.
Delegate Count:
Hillary Clinton: 783
Barack Obama: 709
(Number of delegates needed to win: 2,025)
Check out our complete coverage at RTÉ.ie/uselection.
