Just days after convincing the Campaign Finance Board to award him an extra $1.6 million in public matching funds for what he called a tough re-election race, Mayor de Blasio headed to Rhode Island Monday for a family vacation.

“It’s unfortunate that the mayor made a strong case for additional matching funds by saying he had a competitive race and then took off on vacation,” said Dick Dadey, director of the government watchdog Citizens Union.

“The argument that he needed it for a competitive election doesn’t hold together very well.”

The Democratic primary will be held on Sept. 12, a little more than three weeks after de Blasio’s return on Friday.

It’s rare for candidates to take vacations so close to an election — unless, of course, they think they can’t lose.

Although de Blasio qualified on Aug. 3 for matching funds under the generous regulations of the Campaign Finance Board, he was under no obligation to take the money.

Other heavy favorites in the past have declined, including former City Council Speaker Christine Quinn in 2009.

CFB rules stipulate that matching funds will be capped at 25 percent if a candidate faces minimal opposition, but de Blasio argued that his chief Democratic rival, former Councilman Sal Albanese, posed a serious threat.

The board agreed.

As a result, the mayor received about $1.6 million more in taxpayers matching funds than the $958,000 he would have gotten.

In financial terms, the Democratic primary is about as level as a seesaw.

Records show that the mayor had $4.9 million in his campaign account as of last week after receiving the matching funds. Albanese, who has yet to qualify for matching monies, had just $5,397.

“He has more than enough money to get his message out,” Albanese said, charging that de Blasio is taking taxpayers for a ride. “His [public funds] could have gone towards improving city services.”

When asked to respond to the critics, de Blasio campaign spokesman Dan Levitan said, “They can’t challenge his record on the issues, so the silly season has begun.”

CFB spokesman Matthew Sollars said, “Public-funds payment determinations by the board are based on . . . objective criteria and nothing else.”