Jessica Biel is bringing "SexyBack" ... and side.

Justin Timberlake's wife hit the red carpet for the Los Angeles premiere of "Hitchcock" last night -- where she was showing off some serious skin and her giant rock.

While Jessica's dress was all business (and too much fabric) in the front, when she posed in profile or turned around, it was an entirely different story.

Biel was flaunting some side-boob in the black Gucci gown -- and when she turned around, she revealed a sexy, backless look.

And while all eyes were on her skin, her massive engagement ring and new, diamond wedding band were just as distracting.

Check out more photos from the red carpet above -- including shots of Jessica with costars Toni Collette and Helen Mirren. Plus, see what Biel changed into for the after-party.

"Hitchcock" opens Friday.

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