The ballet world today is afflicted by a scourge of premature debuts. Time and again, unfledged talents have been thrust into demanding roles at enormous physical cost and artistic shortfall. Over the weekend, though, New York City Ballet’s Ashley Bouder and Sara Mearns both made astute and well-prepared debuts as Odette/Odile in “Swan Lake.”

Each performance had its inevitable quotient of flubs or miscalculations, but these were minor.I was left with the impression that both dancers had worked very hard and conscientiously. Each achieved a real success.

Ms.Mearns is only in her second year with the company. Dancing Saturday afternoon, she demonstrated considerable traction on the role, and it seemed well within her technical abilities.

Ms. Mearns’s long and elegant arms allowed her to begin the White Swan solo arrayed in a stunning pose. During the solo, her leg rose high and easily to both sides, although her phrasing of the arabesques was too choppy. In the Black Swan coda,she substituted pique turns for a full sequence of fouettes. This didn’t bother me at all: Indeed, the ability to perform all 32 fouettes has become a specious yardstick for this role. More worthy of remedial attention was her lax batterie in the White Swan coda.

Ms. Mearns was partnered sympathetically by Nilas Martins. Although technically Mr. Martins ranged from honorable to pedestrian, he was able to take the audience inside his head; his economical control of gesture allowed us to register emotional truth rather than surface accuracy.

Ms. Mearns, too, demonstrated surprising dramatic effectiveness when recalled by Von Rothbart from her first encounter with Prince Siegfried; when she pleaded with Siegfried for clemency for her flock; and when, in the final scene, she relayed to her sister swans how Siegfried had betrayed her with Odile.

Even without expanding into the high and elongated arcs that are now endemic to the vocabulary, Ms. Mearns knows how to achieve length in compact and traditional poses. She also took full advantage of Mr. Martins’s piloting of the overhead lifts to achieve a huge reach and stretch in the air.There was a slow, probing expressivity to her legs in the adagio.

Ms. Bouder is not the first NCYB ballerina I’d think of as a candidate for Swan Queen; a rather hard-driving technician, she is more of a Firebird than an Odette. At the same time, there is a slightly neurasthenic tension to her that makes her dramatically compelling.

Performing Friday night, Ms. Bouder was alert to shifts of tone and momentum in the dual role. For instance, in the gambit by which Odile attempts to dissolve into a simulacrum of Odette before the wavering eyes and conscience of Prince Siegfried, her arms were instantly weighed down by an oppressive burden of sorrow.

For most of the ballet, however, Ms. Bouder concentrated on technical and aesthetic accuracy, wisely trying to dance the role as well and as idiomatically as possible rather than trying to impose an ambitious stylistic or emotional outpouring. At times her articulation was a little too clipped, particularly in the White Swan adagio. It was played fast, as it always is at NYCB, but not excessively so. Ms. Bouder doesn’t yet know, as do the older, more experienced Odettes at NYCB, how to find breathing space in a fast tempo.

Over the span of her performance there were a few instances of overkill. She didn’t flap or quiver needlessly, but sometimes her arms and hands were a little froufrou. She was intent on dazzling her audience with her batterie in the coda, and she certainly did, but the speed and quantity of beats proffered didn’t seem to allow her to fully point her feet.

In the final scene of irrevocable farewell, all technical difficulties behind her, Ms. Bouder now loosened up dramatically. Together with her Prince Siegfried, Benjamin Millepied, Ms. Bouder achieved a real emotional potency.

Mr. Millepied’s portrayal, though, was too anecdotal and realistic. His Siegfried seemed to be a product of the Jerome Robbins repertory in which he frequently stars. Throughout the performance he seemed to want to let us know what his Prince was “feeling” – rolling his eyes at his mother when she insisted he find a bride – rather than surrendering some verisimilitude for the artistic truth that would arise from a more reserved and selective emotive palette. His reactions were too rapid and busy to suggest balletic nobility. His technique is a bit flyaway to manifest fully the seigniorial timbre of the role’s technical displays, but he danced honestly.

Throughout both debut performances, it was refreshing to watch the way both Ms. Bouder and Ms. Mearns were able to exploit the youthful pliancy of their backs to approach the iconographic plastique of the role’s Russian prototype.

It seemed to me that as NYCB’s “Swan Lake” run has progressed, the company has become more comfortable with this fairy tale’s drama; the ballroom unmasking now comes to the properly turbulent boil. The corps of swans also danced this weekend with real distinction.

City Ballet’s winter repertory runs until February 26 at the New York State Theater (Lincoln Center, 212-870-5570).