Levi Colwill and James McClean were embroiled in a heated on-field bust-up just three minutes into the Blues' 2-2 draw with Wrexham.
Colwill, 21, reacted angrily to a late challenge by the Irishman, grabbing his shirt by the collar before sparking a brawl between the two sides.
Enzo Maresca's side had to rely on an 82nd-minute equaliser from Lesley Ugochukwu to spare their blushes at the Levi's Stadium, in Santa Clara, California.
The Blues had taken the lead with 10 minutes to go in the first half through Christopher Nkunku, who fired into the corner after the Welsh outfit failed to clear Reece James' corner.