Flashback: Carrie Underwood, Jennifer Nettles Cover Dolly's '9 to 5'

Singers trade lines on the Grammy-winning classic in an unrehearsed Opry performance

In early 1981, thanks in part to the film Urban Cowboy, Billboard's pop singles chart was routinely peppered with huge country crossover hits. In December 1980, another film with a country element to it turned one of its stars, singer-songwriter Dolly Parton, into Hollywood royalty and sent the self-penned theme song for her film, 9 to 5, to the tops of both the country and pop charts.

With co-stars Jane Fonda and Lily Tomlin, Parton propelled 9 to 5 to a $100 million take at the box office, and the empowering title tune, which sold more than a million copies, was nominated for an Academy Award. The single, which opens with the sound of typewriter keys being struck (which Parton conceived by clicking her long, acrylic fingernails together), was also nominated for four Grammys, winning two in the country categories. A short-lived television series (starring Parton's sister, Rachel Dennison) and a 2009 Broadway musical followed. A smash hit throughout the world, "9 to 5" remains one of Parton's most significant contributions to popular culture, and has been referenced in everything from The Simpsons to Sesame Street.

In 2014, Sugarland singer Jennifer Nettles appeared on the Grand Ole Opry and performed the song as a solo act – for about a minute, anyway. As she approached the second verse, Nettles introduced a surprise guest: Opry member Carrie Underwood. Tearing through the verse and then the chorus, Underwood and Nettles stayed true to the song's essence, and then each put their own vocal spin on it as they ad-libbed to the end. "Not bad for no rehearsal," Underwood said as the crowd roared its approval.

The duo may not have had any rehearsal, but it wasn't Underwood's first "9 to 5" gig. She included the song as a special fan-club-voted addition to her set list during select dates of the 2010 Play On Tour.

Underwood returns to perform at the Grand Ole Opry on Tuesday, June 9th, just ahead of the CMA Music Festival, where she'll be among the acts taking the LP Field stage on Saturday, June 13th.