The 32-year-old star is seen lip-syncing 'Perfume', which was co-written written by Furler in a video clip posted online. The Australian singer's voice can be heard in the clip, reported Radar Online.
Furler, 38, featured along with Spears on an acoustic version of the 'Perfume' released in January.
"I'm second hand embarrassed," commented a follower of the Spears fan Instagram account that posted the clip, while another wrote, "Poor Britney."
Spears did not miss a beat, holding her head high as she walked around the stage.