Tomorrow’s voter turnout may hit an all-time low, with no major contest atop the Democratic mayoral ticket.

Experts see just 400,000 to 450,000 deciding the four-way races for city comptroller and public advocate and the heated battle among Richard Aborn, Leslie Crocker Snyder and Cy Vance Jr. to replace Robert Morgenthau as Manhattan DA.

With Comptroller Bill Thompson expected to beat back Councilman Tony Avella for the mayoral nod, turnout should hover between 15 to 18 percent.