The duo was all smiles when posing for photographers at the screening, which took place on August 18, reported Aceshowbiz.
Stewart, 25, looked chic in a floral short jumpsuit by Zuhair Murad with a deep plunging neckline. She sported catseye eyeliner and donned black Jimmy Choo shoes.
Lautner, 23, opted for a semi-casual style with a white shirt, a blue suit and black pants.
Stewart was also joined by her "American Ultra" co-stars at the red carpet event.
She posed together with Jesse Eisenberg, Connie Britton, Topher Grace, Tony Hale and John Leguizamo for a group photo.
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"American Ultra" centres on Mike (Eisenberg), a seemingly hapless and unmotivated stoner whose small-town life with his live-in girlfriend, Phoebe (Stewart), is suddenly turned upside down.
Unbeknownst to him, Mike is actually a highly trained, lethal sleeper agent. In the blink of an eye, as his secret past comes back to haunt him, Mike is thrust into the middle of a deadly government operation and is forced to summon his inner action-hero in order to survive.