Green’s Dictionary of Slang

blow-out n.3

[blow v.1 (5a); orig. jazz use; when two bands staged a competition, the winner was to said to blow its rival out of the house; thus the defeat itself was a blow-out]

a comprehensive defeat.

Show quotations
Lott & Lieber Total Impact 213: Our 55-10 blowout of the Denver Broncos [HDAS].
[US]Myers & Workman Kick 160: By the time we reached the sideline, the Golden Eagles [soccer team] were already up 1—0. This is going to be a blowout, I thought.