William Zeckendorf, a partner at Brown Harris Stevens, has made a $35.5 million killing selling two apartments in less than a year — all thanks to a rival firm.

Zeckendorf sold his co-op at 927 Fifth Avenue on Wednesday for $34.6 million. A broker for Brown Harris Stevens rival, The Corcoran Group, brought in the buyer, Scott Bommer, founder of the hedge fund SAB Capital.

Zeckendorf paid $29.1 million for the co-op, which had belonged to the late banker Bruce Wasserstein. The building is also home to two New York City icons — Mary Tyler Moore and Pale Male, the famed red-tailed hawk.

Last December, Zeckendorf also sold out of a building he co-developed, 15 Central Park West.

He had purchased a penthouse in pre-construction for $10 million and sold it for $40 million.

The 4,024-square-foot apartment sold for $10,200 a square foot — a city record.

Again, a Corcoran Group broker brought in the buyer: Taiwan-born Min Kao, co-founder of Garmin Corp., which makes GPS systems.

Zeckendorf did not return calls.

Pam Liebman, CEO of the Corcoran Group, declined to comment.