"Sugar" Shane Mosley won the first round against Don King -- a judge refused to let King shut down Mosley's comeback, but in the process also crapped all over the fight.
The ruling came down in federal court in Miami where King failed to get the injunction he sought ... believing Mosley's opponent, Ricardo Mayorga, is still under contract with him. The judge said allowing the fight would not damage Mayorga's career in the future ... because his career is almost over.
The judge said of the 41-year-old boxer ... "The undisputed evidence is that Mayorga is not ranked, that he is not at the peak of his physical capabilities and that whether he will participate in any future bouts is purely speculative."
King can still try to prove he has a valid contract with Mayorga, but it won't affect Saturday night's fight at the L.A. Forum ... and, by the way, sounds like there are plenty of seats available.
During testimony, Mosley said only 2,000 to 3,000 tickets had been sold -- and he's even left a few freebies on park benches around L.A. to drum up interest.