Frustration with New York City’s unaffordability and its aggressive police tactics is elevating Bill de Blasio, once dismissed as a left-leaning long shot, into the lead of the Democratic mayoral primary field, according to a poll by The New York Times and Siena College.

Christine C. Quinn, the longtime front-runner in the nomination contest, is now lagging far behind Mr. de Blasio and struggling to connect with members of her own party: forty-five percent of likely Democratic voters view her unfavorably.

With 11 days remaining until the primary, the new survey shows a drastically reshaped race as a broad cross-section of voters embraces Mr. de Blasio’s candidacy. It found that 32 percent of likely Democratic voters supported Mr. de Blasio, who is the city’s elected public advocate, compared with 18 percent for William C. Thompson Jr., the former comptroller, and 17 percent for Ms. Quinn, the speaker of the City Council.