Sarah Jane Nader flashed her rock-hard abs in a tiny tank top … and yet it’s her hand-holding with her “Dancing With the Stars” partner, Hailey Bills, that captured eyes this time.

The reality TV star left rehearsal hand in hand with Hailey later Thursday night … big grins on their faces while they posed for the camera.

Like we noted … SJN’s decked out in a barely-there top and blue sweatpants — while Hailey looked every bit a pro dancer in her all-black ensemble and white tennis shoes.

The duo posed for a few snaps before walking off with their hands still clasped.

As we reported … Sarah and Hailey are joining an exclusive club on the 35th season of ‘DWTS’ — becoming the third same-sex couple in the competition’s history.

JoJo Siwa and Jenna Johnson danced together in season 30 … while drag queen Shangela cut a rug with Gleb Savchenko in season 31.

Sarah told People it’s an “honor” to dance with Hailey … adding that they “probably hit a new frequency in the dance studio, screaming” when they found out. Plus, Hailey added the pair are the “luckiest girls ever.”