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.
Two second-half goals from Luke Bolton and Jack Marriott nearly secured Wrexham a stunning win, but despite the draw, Colwill and McClean's scrap overshadowed proceedings.
Levi Colwill and James McClean had to be broken apart after just two minutes of Chelsea's 2-2 draw with Wrexham
Colwill, 20, reacted angrily to a late challenge from McClean, grabbing him by the collar
Lesley Ugochukwu scored late on for the Blues to save them from an embarrassing defeat
McClean, who hit the news at Euro 2024 for his criticism of Declan Rice, was given the captain's armband for the League One side's clash with Chelsea.
His early challenge on Colwill seemed nothing other than a mistimed tackle, but the English defender seemed to take issue with the former Ireland international.
After Colwill initiated the shirt-grabbing, the pair started to wrestle each other before players and staff from both sides rushed to intervene.
It took several players from both sides to tear the two apart, but they left the incident without punishment from the referee.
McClean is known for his aggressive nature with the winger getting involved in plenty of bust-ups during his time in the Premier League with West Brom and Sunderland.
In 158 appearances in the league, McClean picked up 29 bookings as well as a solitary red card.
The match in the United States was Enzo Maresca's first game in charge of the Blues
The match, played near San Francisco, was the first of Maresca's reign at the Blues, with this match the start of a five-game US pre-season tour.
Chelsea will face off with the likes of Celtic, Club America, Manchester City, and Real Madrid across the next 11 days.
Meanwhile, Wrexham - who are co-owned by Hollywood stars Ryan Reynolds and Rob McElhenney - have now played two matches of a three-game tour in North America.