The United States, fueled by goals from Gio Reyna and Folarin Balogun, beat Paraguay 2-1 on Saturday in a clash of World Cup-bound teams marred by a stoppage time brawl.
Balogun scored the game-winner in the 71st minute in a match that had been tied since the 10th.
Mauricio Pochettino's men had successfully held off a determined late assault by Paraguay when things suddenly turned ugly in injury time.
Paraguay's Gustavo Gomez had picked up the ball for a throw-in when American Alex Freeman apparently disagreed and tried to grab it. A shoving match ensued with players rushing in from both sides.
Unused Paraguay substitute Omar Alderete was shown a red card and US midfielder Cristian Roldan and Paraguay's Junior Alonso each received a yellow as order was restored and the final minutes played.
The United States, unbeaten in their last three games, had taken the lead in the fourth minute as Reyna, making his first international appearance since March, headed in off the bottom of the crossbar.
Paraguay had struggled to clear the first corner of the match. Shots from Sergino Dest and Roldan were both blocked, but the Americans were still threatening and when Max Arfsten floated the ball into the area again Reyna was there to head it home.
Paraguay responded just six minutes later as Alex Arce headed in from close range after Miguel Almiron got free down the left side and fired over a pinpoint cross.
But Balogun put the United States back in front in the 71st firing home a pass from Reyna from the centre of the box.
The match at Subaru Park, home of Major League Soccer's Philadelphia Union, was part of both teams' preparation for the 2026 World Cup.
The United States were guaranteed a spot in next year's global showpiece as co-hosts with Canada and Mexico while Paraguay came through South American qualifying to book a ninth World Cup appearance, and their first since 2010.
Both teams will play again on Tuesday when the United States face Uruguay in Tampa, Florida and Paraguay take on Mexico in San Antonio, Texas.