De Blasio leads the Democratic primary field with 36 percent support, nearing the 40 percent threshold he'd need to avoid a runoff. New York City Council Speaker Christine Quinn (D) and former city Comptroller Bill Thompson lag behind at 21 percent and 20 percent support, while former Rep. Anthony Weiner (D-N.Y.) has slid to 6 percent support.

If the race does go to a runoff, de Blasio leads all comers by more than a 20-point margin.

That's a big reversal in a few short weeks: De Blasio was sitting in fourth place in many polls earlier this summer.

The poll of likely Democratic primary voters was conducted from Aug. 22-27 and has a margin of error of 4 percent.