The Radiohead frontman’s calming voice soothed the crowd during an interruption midway through the band’s set.
Rock and roll titans will share the stage in Brazil and Argentina next year.
The band responded by playing three encores.
The band’s concert had been canceled due to the city’s ban on events featuring synthesizers and samplers.
The ban prohibits any event in which “synthesizers or samplers” are the primary instrument.
The young fan also plucked along at a bass that was way too big for her.
Former frontman of Soda Stereo was one of the most influential Latin American musicians.