Prior to the ceremony's start at the MGM Grand Garden Arena, the duo was awarded the Vocal Event of the Year prize for the duet We Were Us.
Lambert, who is nominated for seven ACM Awards, scored her 16th trophy with the win.
The Band Perry kicked off the evening performing their hit Chainsaw, while duo Florida Georgia Line rocked with their tune Stay, Brett Eldredge took the stage with Beat Of The Music and Brad Paisley sang his track River Bank for the first time on Tv.
Blake Shelton also took a break from hosting duties to perform his song My Eyes with Gwen Sebastian.
Shelton and co-host Luke Bryan, who are both nominated for the Entertainer of the Year prize, are emceeing the ceremony for the second year in a row.