Mayor Bill de Blasio added nearly 300 affordable-housing units toward his goal of creating or preserving 200,000 low-cost apartments within a decade with the groundbreaking Monday of a project near the Barclays Center in Brooklyn.

Pacific Park Brooklyn, formerly known as Atlantic Yards, will feature a building with 298 units reserved for low- to middle-income residents, or families of four making between $32,000 and $138,000.

Developers must prioritize low-cost housing alongside more expensive, market-rate complexes, de Blasio said at a news conference at the Prospect Heights site.

"I did support this development from the beginning because I saw what was happening around us," he said, "and I knew if we didn't change the dynamic, people would just be priced out over and over again."

De Blasio has pushed affordable housing as a key component of the complex -- which includes Barclays Center, home to the Brooklyn Nets and the arena at the center of the city's bid to host the 2016 Democratic National Convention -- in part because eminent domain was used to remove former residents.

The city Housing Development Corporation is contributing a $73 million tax-exempt first mortgage for the new building, named 535 Carlton for its address, as well as $11.75 million in subsidy financing.

The first residence began construction at Pacific Park in 2012. Ground is to be broken for a third building next June. The entire complex will include 6,430 apartments, with one-third categorized as affordable.

De Blasio expects to have financing and permits secured for 16,000 affordable housing units by the end of this year.