Ken Egan lost out on a split decision to Ukrainian light-heavyweight Vyacheslav Shabranskij as his Miami team suffered a 5-0 defeat to Los Angeles on Sunday night.
Egan was hoping to record his second WSB victory in the ring and his third win overall - one of his wins was via a walkover - but Kiev-born Shabranskij edged the five-rounder (48-47,46-49,49-46).
Egan's Irish team-mate John Joe Joyce, who is also signed with Miami, ceded a walkover to LA middleweight Russell Lamour after picking up the flu.
Sundaynight's win moves Los Angeles ten-points clear of third-placed Miami at the top of the table in the WSB Americas group with five matches left.
The winners in the Asian, Americas and European groups plus the best runner up qualify for the WSB Team Championships semi-finals.