Getty / Hot Girl Productions Composite

Megan Thee Stallion was front and center, cheering on her beau, Klay Thompson , for his NBA season-opener when he and his Mavs got blown out by over 30 points -- and she's doubling down her affection in a new single!!!

On Friday, Megan unleashed her "Lover Girl" single -- independently released on her Hot Girl Productions imprint -- lyrically gushing over Klay's moves off the court ... "My man, my man, my man, my baby, my baby / D****n' me down, spoiling me, driving me crazy."

Meg proudly refers to Klay as "her n***a" but says he never stoops low and labels her a "b*tch" ... but raps how the Splash Brother has no issues turning her lady parts into "Splash Town" -- backing up all the liquid language she flexed on her Diamond-selling collab wit

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