Naturally, London was the locale for the premiere, where Knightley donned a stunning pearl-encrusted, buff-hued Chanel Haute Couture gown with cutouts on the sides and back, and a low V-shaped neckline, all of which were partially concealed by strands of more pearls.
The English beauty, who is the face of Chanel's Coco Mademoiselle fragrance, wore her recently chopped off locks in a loose and modern do and paired the stand-out frock with black platform pumps.
Mulligan's ensemble, on the other hand, was rather disappointing, especially because she usually excels in the style arena.
This time, however, the pixieish actress wore an odd pleated halter-neck Vionnet dress with a bold red-and-black zigzag pattern around her belly, a thick black stripe below her hips, and a rose-hued block around her ankles.
To top it off, 25-year-old Mulligan opted for Giuseppe Zanotti for Vionnet metallic heeled sandals with a basket-weave bottom and a weird hairstyle that consisted of pinned-back curls that looked somewhat wet and messy and showed off her dark roots.
So, while we're all about trying something new, we think Mulligan might have missed the mark on this one.
Do you agree? Let us know what you think about both ladies' ensembles in a comment below.
In related news, check out behind-the-scenes pictures of Knightley's new Chanel campaign.