Manny Pacquiao K.O.'d Diddy Mansion Deal ... Buys Other Mansion Instead

Remember when Manny Pacquiao rushed in and pulled the trigger to buy Diddy's old mansion in Beverly Hills last year??

Turns out, Manny 86'd the deal at the last minute ... and our sources tell us it's all because he wouldn't "come out of hiding" to sign the closing docs in the weeks before the Mayweather fight.

Our sources, who were directly involved in the deal, say Manny immediately fell in love with the 10,000 square foot pad -- which was listed at $12.5 million. We're told MP wanted to move in so quickly, the offer was to buy the place fully furnished with all of the existing furniture.

But as one source put it, "Manny had to go into hiding right before the fight which was right at the time of closing and his managers wouldn't proceed with the deal without him."