Two American Ballet Theater dancers practiced one of the notoriously difficult pas de deux from Alexei Ratmansky’s “The Nutcracker” this month, in a big studio near Union Square. Cory Stearns, a principal dancer since 2011, offered a steady hand and princely smile to his partner, Hee Seo, a delicate beauty in a rose-colored leotard and a practice tutu that looked as if it had seen better days. Under the benevolent but intent gaze of their boss, Kevin McKenzie, artistic director of the company, they carefully went over every tricky passage, despite that they had performed it several times since its creation in 2010.

After a nod to the rehearsal pianist, the two took a few steps hand in hand, then broke into a slow waltz and bowed ceremoniously to each other. Mr. Stearns put his hands on either side of Ms. Seo’s torso, just below her rib cage, and lifted her, at chest level, up and over to his right, then circled her once with one hand around her waist, her body tilting — intentionally — off-balance. From there, after supporting her in a pirouette, he maneuvered her into a swoon. The transition looked choppy and a little uncomfortable.

Mr. McKenzie, known as a highly skilled partner in his day, stepped in. He placed his hand in a slightly different spot on the ballerina’s waist, allowing her to nestle more comfortably into the crook of his elbow. Mr. Stearns watched, adjusted his stance and tried again. The trouble spot evaporated; both dancers relaxed visibly. The transition acquired a kind of sweep, not without a touch of excitement. “Play with being Fred and Ginger,” Mr. McKenzie said later, “connected at every moment.”