Sabrina Carpenter Sings 'These Boots are Made for Walkin' at Outside Lands Festival

Sabrina Carpenter and Kacey Musgraves killed it at the Outside Lands Music Festival in San Francisco, singing one of the most iconic songs ever ... and the crowd went nuts!

Sabrina and Kacey sang Nancy Sinatra's famous hit, "These Boots Are Made For Walkin'" ... and the only thing that was a little disappointing -- Kacey wasn't wearing boots!

Nevertheless, there was a lot to celebrate ... before taking the stage, Sabrina took a sip from an espresso cup to celebrate her hit song, "Espresso," passing the 1 billion mark in terms of streams on Spotify.

There were a bunch of other stars who performed, including Post Malone, Shaboozey, The Killers, Chappell Roan, Sturgill Simpson and others.

But Grace Jones stole the show. The 76-year-old icon wooed the crowd with amazing costume changes, opening her set 30-feet above the stage. She ended the 1-hour set hula- hooping barefoot wearing a g-string and singing "Slave to the Rhythm."

Post and Sturgill will perform Sunday night to close out the festival.