Sen. John McCain seized command of the race for the Republican presidential nomination early Wednesday, winning delegate-rich primaries from the East Coast to California.
Democratic rivals Hillary Rodham Clinton and Barack Obama traded victories in an epic struggle with no end in sight.
Clinton won the biggest state, California, for the Democrats, capitalizing on support from Hispanic voters.
McCain's own victory in the Republican race in the Golden State dealt a crushing blow to his closest pursuer, former Massachusetts Gov. Mitt Romney.
"We've won some of the biggest states in the country," McCain told cheering supporters at a rally in Phoenix, hours before California made his Tuesday Super. An underdog for months, he proclaimed himself the front-runner at last, and added. "I don't really mind it one bit."
In the competition that counted the most, the Arizona senator had 497 delegates, more than 40 percent of the 1,191 needed for the nomination - and far ahead of his rivals.
Even so, Romney and former Arkansas Gov. Mike Huckabee said they were staying in the race.
Neither Clinton nor Obama proclaimed overall victory on a Super Tuesday that sprawled across 23 states, and with good reason. Obama won 11 states and Clinton eight plus American Samoa. Shortly after 1 a.m. EST, winners were still to be declared in Missouri, New Mexico and Alaska.
"I look forward to continuing our campaign and our debate about how to leave this country better off for the next generation," said the former first lady, looking ahead to the primaries and caucuses yet to come.
Obama was in Chicago, where he told a noisy election night rally, "Our time has come. Our movement is real. And change is coming to America."
Polling place interviews with voters suggested subtle shifts in the political landscape.
For the first time this year, McCain ran first in a few states among self-identified Republicans. As usual, he was running strongly among independents. Romney was getting the votes of about four in 10 people who described themselves as conservative. McCain was wining about one-third of that group, and Huckabee about one in five.
Overall, Clinton was winning only a slight edge among women and white voters, groups that she had won handily in earlier contests, according to preliminary results from interviews with voters in 16 states leaving polling places.
Obama was collecting the overwhelming majority of votes cast by blacks - a factor in victories in Alabama and Georgia.
Clinton's continued strong appeal among Hispanics - she was winning nearly six in 10 of their votes - was a big factor in her California triumph, and in her victory in Arizona, too.