Also rehearsing Friday: Broadway star Idina Menzel, who's set to sing "Let It Go" from animated film nominee "Frozen"; U2, which is nominated for its song from the Mandela movie, "Ordinary Love"; and rocker Karen O, who is nominated for "The Moon Song" from best-picture nominee "Her."
Menzel was awed by the technology that allowed the Oscar orchestra, playing off-site at the Capitol Records building, to coordinate with her live at the Dolby Theatre.
"Hi, Bill, can you hear me?" she said into the microphone at conductor William Ross, whom she could see on a monitor from inside the theater. "I'm trying to get that telepathic vibe with you because I'm alone up here and this is my first time (on the Oscars).
"You look very handsome," she added.
Karen O, front woman of the rock band Yeah Yeah Yeah's, took notes from director Spike Jonze as she practiced her performance, "The Moon Song" from his best-picture nominee, "Her."
"Spike just asked me to hold the mic a little bit lower, so I need a little more level," she told a sound engineer. Jonze sat in a front-row seat in the audience.
Accompanied by Vampire Weekend's Ezra Koenig on acoustic guitar, O sang the song again and again, sitting on a corner of the stage in a long floral dress, leather motorcycle jacket and killer blue boots.
Williams arrived wearing a polka-dot jacket, patterned scarf and his trademark hat.
