Nick Young's Baby Mama Gives Birth!

It's been a good 24 hours for Nick Young ... because he just became a father AGAIN ... TMZ Sports has learned.

We've confirmed Nick's ex-girlfriend, Keonna Green, gave birth to a bouncing baby girl moments ago!

Green and Young aren't in a relationship anymore but they're on good terms. They already have a 4-year-old son together.

Nick rushed to the hospital late Wednesday night after the Lakers game (they won!) and wanted to be there when his daughter was born! Success!!!