Public Advocate Letitia James didn’t just take $750,000 in public money that she didn’t need for her campaign this year: She spent $500,000 of it on Election Day itself — dumping money she’d otherwise have been obliged to return.

Her gaming of the system is arguably worse than Mayor de Blasio’s: He at least faced a credible general-election challenger. James’ little-known Republican rival, J.C. Polanco, raised just $26,000.

Which means she outraised him by 4,000 percent — yet still got a bath of taxpayer funds.

The law cuts public matching funds by three-quarters if a candidate has no serious opponent. But the legal rules for “serious” are laughable: Merely because Polanco had made many talking-head appearances on NY1 and Univision, James was able to oblige the Campaign Finance Board to pay her the full amount in matching funds.

And on Election Day, she won 74 percent of the vote to Polanco’s 16 percent, with minor-party candidates splitting the rest.

Mayor de Blasio pulled much the same scam to collect big cash during the primaries, when he had no serious opposition.

Comptroller Scott Stringer was the only citywide official to say “no” to padding his campaign outlays at the public’s expense.

The public has an outside chance of clawing back some of James’ windfall: The CFB does post-election audits of campaign spending, and it will certainly give a close look at her last-day outlays. But if she dumped the funds on “legitimate” consultant-cronies, the board may be unable to do a thing.

Then, too, it can take years for a full CFB accounting, especially if a campaign dawdles in sharing its records.

In any case, it’s plain that James was happy to ding the public for every dime she legally could — which is a pretty remarkable approach for the city’s public advocate.