Bill de Blasio leads Republican Joe Lhota among likely voters by 43 percentage points in the race for New York City mayor, an early jolt of positive news for Democrats seeking to recapture City Hall for the first time in 20 years, a Wall Street Journal-NBC 4 New York-Marist poll released Tuesday showed.

Mr. de Blasio, the city's public advocate, is outpacing Mr. Lhota, a former deputy mayor under Rudy Giuliani, 65% to 22% among likely voters, including those who are undecided but leaning toward a candidate. Adolfo Carrión...