Which Oscar nominee made the most dazzling movie debut? Which nominees were co-stars?

Natalie Portman as Nina in "Black Swan;" Annette Bening as Nic in "The Kids Are All Right"

If the Academy gave awards for most distinctive debut performance, then Hailee Steinfeld would certainly win the supporting statuette this year for her role in True Grit and Natalie Portman and Jesse Eisenberg would have Oscars for their movie debuts The Professional (1994) and Roger Dodger (2002). Famously, Portman played the alienated tween taken under the wing of hitman Jean Reno while Eisenberg was the sexually curious teen taken under the wing of his jaded uncle, Campbell Scott. By the same token,  Christian Bale would most certainly have an Oscar for his part as the displaced English boy in the Japanese concentration camp in Empire of the Sun.

The other two leading Oscar contenders, Annette Bening and Colin Firth, had less auspicious debuts. Bening played Dan Aykroyd's wife in the boor comedy The Great Outdoors (1988) while Firth was one of the students  in the hermetic making-of-a-spy drama Another Country (1984).

Bening and Firth were much more memorable in Valmont (1989), which had the bad timing of being the second of the two movies based on Choderlos de Laclos' Dangerous Liaisons.

Among any year's nominees, who made the most remarkable debut?