Retired lawyer Donald Schupak, best known for negotiating the ABA/NBA merger in 1976, put his Upper East Side pad back on the market — for $21 million.
He first listed his home for $30 million back in 2015.
Six years later, he’s knocked off $9 million, but is still working with the same broker, Corcoran’s Amy Katcher.
The floor-through, seven-bedroom co-op at 1050 Fifth Ave. is on the building’s 18th floor.
It is 7,500 square feet and comes with 1,500 square feet of wrap terraces, including almost 100 feet on Central Park.
New windows capture 180-degree Central Park views, along with the George Washington Bridge and the Jacqueline Kennedy Onassis Reservoir, according to the listing.