The Gallup Poll Daily tracking shows the Illinois senator leading Republican presidential hopeful John McCain 50 percent to 42 percent.

Up until the poll from Aug. 30 through Sept. 1, Obama led by no more than 49 percent of registered voters. McCain has had no greater than 48 percent support, which he enjoyed in late April and early May, Gallup said.

"This, in part, reflects movement of voters toward Obama over the course of the Democratic National Convention, a lead which has been sustained in subsequent days," Gallup said in its analysis.

The Daily tracking numbers are based on combined data from Aug. 30-Sept. 1 from a sample of 2,772 registered voters. The maximum margin of sampling error is plus or minus 2 percentage points.