Brent Harrington/CBS Elle King and Miranda Lambert
On Sunday, the pair opened the awards show with a performance of their duet "Drunk (And I Don't Wanna Go Home)," which was released in February.
Lambert, 37, and King, who is expecting her first child, wore matching pink and blue fringed jackets at the Ryman Auditorium in Nashville.
After their rehearsal for the performance, Lambert told PEOPLE, "It was hard."
"I mean, honestly we had never sang it together live at all, and none of us have done shows in a really long time, so it's a weird feeling," she said.
King, 31, added: "It's excitement, but also it's a hard song to sing."
"We did good," she said. "We nailed it. Applause? This feels nice. I think I like that. It's a good thing."
The longtime friends are happy to "have a lot fun together" again after the last year, and they believe they crafted the perfect song to make it happen.
"Even when we're nervous, and we've worked all day and we have hair and makeup and all the things that we're doing, when we get out there to sing together, we kind of come back to the root of it," Lambert said. "And it's fun to sing a song called 'Drunk' with a pregnant lady."
"You know, if I wasn't pregnant, I could be throwing up from drinking, but now it's different," King joked.
"We just keep saying that I'm drinking for two," Lambert cracked.
Kevin Mazur/Getty Miranda Lambert and Elle King
Last year, the ladies were nominated in the music event of the year category for their cover of Elvin Bishop's 1976 hit "Fooled Around and Fell in Love."
This year, Lambert, who is the most-nominated female artist in ACM Awards history with 68, is up for female artist of the year as well as video of the year, single of the year and song of the year for "Bluebird."
Lambert, who is fresh off her best country album win at the Grammy Awards for Wildcard, will team up with The Marfa Tapes collaborators to perform their single "In His Arms" later in the show. (Their album is due out in May.)
Check out PEOPLE's full ACM Awards coverage to get the latest news on one of country music's biggest nights.
Courtesy Sony Music Nashville Miranda Lambert and Elle King in the "Drunk" music video
Leading the list of nominees this year are Maren Morris and Chris Stapleton with six each. Trailing closely behind is Lambert with five nominations, while Ashley McBryde and Thomas Rhett earned four nods each.
Making history this year, four Black artists are nominated for awards: Jimmie Allen, Kane Brown, Mickey Guyton and John Legend, who is a first-time nominee. (Allen and Brown's wins were announced days before the broadcast.)
Also for the first time, every nominated song for single of the year features a woman (Lambert, Morris, Gabby Barrett, Carly Pearce and Ingrid Andress).
Up for the most-coveted entertainer of the year award are Stapleton, Thomas Rhett, Luke Bryan, Eric Church and Luke Combs. (Thomas Rhett and Carrie Underwood shared the 2020 title.) Notably absent from the nominations list is Morgan Wallen, whose eligibility was halted earlier this year after he used a racial slur.
Performances will be taking place across various Nashville venues, including the Grand Ole Opry House, Ryman Auditorium, The Bluebird Cafe, Station Inn, Bridge Building and on Broadway.
The 2021 ACM Awards are airing live from Nashville Sunday from 8-11 p.m. ET on CBS and Paramount+.