Kacey Musgraves - "Kacey Musgraves is a Songwriter First, Singer Second"
Musgraves co-wrote the song with Shane McAnally and Josh Osborne. She and McAnally were also nominated for "Mama's Broken Heart," a song they wrote with Brandy Clark.
"This is crazy," she said in accepting the honor during pre-show ceremonies in Los Angeles. "Thank you so much. The fact that this song was chosen as the best out of so many amazing songs in a year, it just blows my mind. This song has changed my life."
The Texas native then introduced her co-writers.
"I will never forget the day that we were sitting down in the middle of nowhere in Texas, and this song just came to us kind of out of nowhere," she said. "You never know what you're going to get in a co-write, and we tapped into something special that day. I'm just so thankful. I'll never get tired of playing that song. It's so special to me."
McAnally also credited other songwriters who contributed to Musgraves' Same Trailer Different Park album.
"We absolutely have to say thank you to the other two sort of silent co-writers who made this record with us -- Brandy Clark and Luke Laird," he said. "We all five just kind of huddled down and wrote these songs, and it was just a spin of the wheel. We're just obviously completely honored to have this."
Osborne pointed to Musgrave's significance as an artist.
"We felt a tremendous amount of responsibility with this song because we believe in Kacey so much," he said. "So for you guys to embrace it and embrace her, it means everything to us because she is good for our format, and she is good for all music. So thank you so much for giving her the opportunity."