By TMZ Sports

Former three division world champion 'Sugar' Shane Mosley just got hit with a costly hook after a judge ordered him to hand over $300,000 to his ex-wife.

According to docs obtained by TMZ Sports ... Mosley must pay Jin Mosley $180,000 in back child support dating from December 2014 to November 2015. He also has to pony up almost $85,000 for his share of a tax debt the couple owed.

To add insult to injury, Shane's gotta pay Jin's attorney fees to the tune of $50,000. It's been a nasty divorce since jump street -- as we've reported, Shane claims they were never really married since Jin two-timed him.

Last year Jin filed a lawsuit, claiming Shane defamed her when he falsely claimed she was married to another man when they tied the knot in 2002.

Jin claims he knew that her divorce from her previous husband Sanjay Dwivedi was granted in September 2002 ... two months before she married Shane.

Of course, this all became an issue when Shane blasted Jin in early 2015 -- telling multiple media outlets, including TMZ, that his marriage to Jin was bogus from the start because she was already hitched.

Jin admits there's a weird wrinkle to all of this -- because Sanjay got a second divorce judgment in 2006 for unknown reasons ... which may have confused Shane. She says Shane should have known the 2006 judgment was irrelevant because he allegedly saw official documentation which showed the divorce was granted by a judge in 2002. 

This bit of bad news comes on the heels of Mosley's recent twelve round decision loss to David Avanesyan in a WBA final world title eliminator.