Here is the match via youtube:
This bout against Serafim Todorov of Bulgaria, Mayweather lost by a controversial decision (similar to the Roy Jones Jr. decision). Referee Hamad Hafaz Shouman of Egypt mistakenly raised Mayweather’s hand (thinking he had won), while the decision was announced giving the bout to the Bulgarian.
https://www.youtube.com/watch?v=yo3Ar538Sf4