Obama's wins Tuesday in the District of Columbia, Maryland and Virginia gave him 1,215 delegates to Clinton's 1,190 heading into the next round of Democratic primaries in Washington and Wisconsin and caucuses in Hawaii next week, CNN reported.
The victories extended Obama's winning streak to eight.
A candidate needs 2,025 delegates to win the Democratic nomination. While Obama has the edge in pledged delegates, Clinton held the lead when factoring in superdelegates -- party officials and leaders who don't have to pledge their votes publicly and can change their minds, CNN said.
"The change we seek swept through Chesapeake and over the Potomac," Obama told supporters Tuesday night.
McCain has a 812-to-217 lead over Huckabee in the delegate count. To be the Republican nominee a candidate needs 1,191 delegates.
The next races for the Republicans are the primaries in Washington and Wisconsin.