Hillary Clinton and Barack Obama shared the Super Tuesday spoils this morning as one of the biggest voting days in American political history turned into one of the closest-ever electoral struggles.
In an extraordinary and dramatic night, Mrs Clinton won at least eight states, including the big prize of California, and the overall vote by a single percentage point. But Mr Obama swept 13 states.
The former First Lady appeared to have a slight edge in the number of delegates secured.
But the two candidates are now neck and neck in a battle that will continue well into the spring and possibly even to the Democratic national convention in August when the delegates meet.
Both candidates went into Super Tuesday, when millions voted in 22 states, with two states apiece.
Since winning convincingly in South Carolina, Mr Obama has wiped out Mrs Clinton's long-held national poll lead.
Super Tuesday, effectively a national primary, did little to clarify one of the most fascinating American electoral contests in living memory.
To win the nomination, a candidate needs 2,025 delegates. Neither senator has even a third of this number even though well over half the states have voted.
Mrs Clinton won her home state of New York, New Jersey, Massachusetts, Oklahoma, Tennessee and Arkansas, Arizona and California.
Mr Obama took his home state of Illinois, Georgia, Alabama, Delaware, Connecticut, Minnesota, North Dakota, Idaho, Utah, Kansas, Missouri, Colorado and Alaska.
Votes were still being counted in a tight contest in New Mexico. With delegates being shared out proportionately, winning states was less important than scoring big margins.
There was also a furious battle to shape media coverage and therefore public perceptions of who had won.
The Clinton campaign trumpeted the California result by announcing: "After showing that she can win in red states and blue states, in rural areas and big cities and from East to West and everywhere in between, Hillary Clinton ended a truly super Tuesday with a big California win."
He added: ""If this ends up being a draw…we think that this is a remarkable night for us. February 5th was always seen as a tough night and as recently as two weeks ago they were saying they hoped to wrap it up tonight".
An ebullient Mrs Clinton appeared before cheering supporters in New York and said: "I look forward to continuing our campaign and our debate about how to leave this country better off for the next generation because that is the work of my life."
She added: "Because you know that politics isn't a game. It is not about who is up or down. It is about your lives, your families, your futures."
Soon afterwards, Mr Obama took to the stage in Chicago to tell a huge crowd: "There is one thing on this February night that we do not need the final results to know. Our time has come. Our movement is real and change is coming to America. What began as a whisper has now swelled to a chorus that cannot be deterred."
David Axelrod, Mr Obama's chief strategist, said that "we have the momentum moving forward" and although "we're still the underdogs…we leave here with new confidence and a new resolve".
Before the polls closed, both the Obama and the Clinton campaigns predicted a long night with an inconclusive verdict that would take their contest on until the spring.
Mr Plouffe had said: "My guess is we'll have a good night and we'll probably end up with a split decision."
He added: "Maybe this goes to August."
After Super Tuesday, the candidates had no time to rest. Mr Obama was due to fly to Washington for Senate business on Wednesday before heading to Louisiana the same day and then on to Washington state and Nebraska.
All three states have primary contests on Saturday.
Mr Obama, who hauled in a million dollars a day in January - twice as much as Mrs Clinton - holds an advantage in the money stakes.
He is also in a strong position for "Potomac Tuesday" next week when Maryland, Virginia and the District of Columbia vote. Opinion polls out him ahead there.