WASHINGTON -- Landslide margins among black voters fueled Barack Obama to his win Saturday in South Carolina's Democratic presidential primary.

It was enough to overcome the edge that Hillary Rodham Clinton and John Edwards had among whites.

As expected, blacks made up half the voters in Saturday's contest, by far the biggest share in any presidential contest so far this year.

As in Nevada's Democratic contest last weekend, Obama won about eight in 10 votes cast by black voters, with black men and women supporting the Illinois senator by about that same margin, according to preliminary results from exit polls of Democratic voters conducted for The Associated Press and the networks.

Clinton and Edwards split the white vote about equally, with each getting a little less than 40 percent getting about about 25 percent.

Obama got more than a third of the white vote in the year's first contest in Iowa, where nearly all the voters were white -- enough for him to win in that state.