LEANN RIMES performed a duet with 13-year-old CARLY ROSE SONENCLAR on Wednesday night's "X Factor". It wasn't Carly's best performance, and it wasn't LeAnn's either.

In fact, LeAnn's performance was so weird that there was talk she might have been either DRUNK or messed up on something else.  But she denies that.

LeAnn Tweeted, quote, "In my 18 years of performing, I've never been anything but professional onstage." Although that clearly doesn't extend to her private life.

She adds, quote, "It's a shame that gossip and lies are overshadowing the performance of Carly, a very talented young girl. It was an amazing opportunity to share this experience with Carly and I know I'll be watching for her to win tonight."

Carly's performance may have been hampered by the fact that LeAnn was "off" the whole time.  Maybe LeAnn was just nervous, and didn't want to admit it.

By the way, TMZ is reporting that LeAnn, quote, "made a plate of food backstage and spilled it everywhere." I guess it's supposed to support the theory that she was drunk.