Although CNN projections showed Obama winning more states overall, Clinton claimed victory in several key states with higher delegate counts, including New York, which she represents in the Senate, and California.
Latest estimates suggest the pair could be separated by as few as 20 of the 1,678 delegates at stake on Tuesday as 24 states and the U.S. Pacific territory of American Samoa went to the polls.
Clinton appeared before supporters in New York Tuesday night, saying, "Tonight in record numbers, you voted not just to make history but to remake America.
"After seven years of a president who listens only to the special interests, you're ready for a president who brings your values and your dreams to your White House," she said.
She capped her speech with the words: "I know we're ready."
In Chicago, Illinois, Obama took the stage to the strains of U2's "It's a Beautiful Day" Tuesday night, claiming that "our time has come ... and change is coming to America."
"There is one thing on this February night that we do not need the final results to know," he said, noting that all the votes on Super Tuesday had not been counted. "Our time has come.
"What began as a whisper in Springfield has swelled to a chorus of millions calling for change," Obama said. "This time can be different because this campaign for the presidency of the United States of America is different."
Delegates Update (Updated Feb. 7, 2008)
DEMOCRAT (Needed to Win = 2,025):
Hilary Clinton (823): Pledge: 630; Superdelagates: 193
Barrack Obama (741): Pledge: 635; Superdelagates: 106
REPUBLICAN (Needed to Win = 1,191):
John McCain (680): Pledge: 663; Unpledged RNC: 17
Mitt Romney (270): Pledge: 261; Unpledged RNC: 9
Mike Huckabee (176): Pledge: 173; Unpledged RNC: 3
Understanding Delegate Definitions:
Pledged delegates: Won by candidates in primaries and caucuses; pledge to support their candidates at the national conventions.
Superdelegates: Democratic officeholders and party officials guaranteed national convention seats; can support the candidate of their choice.
Unpledged RNC member delegates: Republican party officials guaranteed national convention seats; can support the candidate of their choice.