The two Democratic contenders for the party's presidential nomination will split the vote and Super Tuesday's results will be inconclusive, Barack Obama said.
The 46-year-old Illinois senator, who would be the first African American president of the United States, predicted the nomination race would continue and no front-runner would emerge, despite more than 20 states voting in what is the closest to a national primary election America has ever seen.
His rival, former First Lady Hillary Clinton, and many political pundits, agreed. Mr Obama said a "split decision" was likely.
In California, a key state with 370 Democratic delegates on offer, a recent surge has seen Mr Obama leap to a statistical tie with Mrs Clinton who has been ahead for weeks. He also pulled level in a national poll.
Earlier, asked about the potential of a "dream ticket", which would include both Mr Obama and Mrs Clinton as president and vice-president, Mr Obama insisted he was concentrating on winning the party's nomination first.
Speaking in West Newton, Massachusetts, Mr Obama told CNN: "I think there's some gamesmanship going on right now."
Smiling, he added: "It would be presumptuous of me to suggest that Senator Clinton wants to be my vice president."
Referring to a Clinton supporter who implied that Mrs Clinton was likely to ask Mr Obama to be her vice-president but that Mr Obama would not ask Mrs Clinton, he said: "I think that folks on her side should recognise that we're in a tough contest right now.
"If she wins the nomination then they can start speculating on who the running-mate will be.
"I'll make sure I focus on the nomination and once we do that we'll bring the country together and we'll all go after winning the White House."
