Slay is a fine public official -- one who has enjoyed good rapport with blacks, by the way -- but it's not as if he's riding in as an outsider. He was aldermanic president during both the Bosley and Harmon administrations, and there weren't screaming feuds every day.
Other than race, what could possibly account for Slay's taking almost all of Harmon's white support?
It appears that Slay is poised to be the next mayor. On the other hand, as Zogby noted, Bosley should not be counted out, because of the heavy (19 percent) undecided numbers. Blacks have often been under-represented in pre-election polling.
Personally, I prefer Bosley, but there's a larger point here. If Bosley should pull out a come-from-behind win, it would almost certainly be made possible by a large black turnout, and the big story will be race.