Mayweather vs. Pacquiao -- Fire Sale On Tix ... Investors Losing Big $$$

It was supposed to be the hottest ticket of the year ... but it's gone cold ... and now multiple investors who tried to flip tickets to Mayweather vs. Pacquiao tell TMZ Sports they're losing BIG MONEY.

As we previously reported, ringside seats hit the market for upwards of $80,000 ... and face value of the crappy seats originally went on sale for $1,500.

A bunch of high profile ticket brokers and investors bought up as many tickets as they could get -- thinking it was a sure bet ... since interest in the fight has been through the roof.

But it just ain't panning out -- with one broker blaming the high prices and the fact that tickets only went on sale 10 days before the fight -- and investors are losing their asses.

One company told us they initially bought 80 tickets ... but only moved 20 ... and now they're holding the bag on 60 high-priced stubs.

"It's an embarrassment. We lost a significant amount of money," one broker tells us.

Same story for another ticket broker -- who tells us things have gotten "desperate" and they're slashing prices like crazy.