Kristen Stewart walked the red carpet solo at last night's Runaways premiere presented by Klipsch ... but she did it looking fierce! Rob was noticeably absent, but Taylor Lautner turned out to support his girl!

KStew's really been making an effort with her image -- smiling, dressing sexy, giving good interviews -- what's going on?!

And now, Kristen's taking the time to get all dolled up and her man leaves her lonely? We're guessing it's because Rob's off doing press for Remember Me and couldn't make it last night. Which reminds us ... this couple will have movies going head-to-head at the box office this weekend. Who do you think will come out on top?

Meanwhile, Dakota finally looked age-appropriate and adorable in this short metallic dress.

It seems Kristen couldn't last in her sexy red number ... she slipped out of her dress and into some jeans for the after-party. Still sexy!