Mars provided the night's big upset, taking the album of the year trophy that most critics assumed would go to Lamar's rap tour de force, Damn.
In the end, voters found Mars's crowd-pleasing R&B more palatable, while Lamar dominated the rap categories.
Alessia Cara won best new artist - making her the only female artist to win a major prize.
Stars like Lady Gaga, Kesha, Lorde and SZA were overlooked, with only 17 awards (out of a total of 86) going to women or female-fronted bands.