"As long as we keep scoring goals, I think we'll be OK," midfielder Julian Gressel said with a smile.
United jumped ahead 4 minutes into the game off an own-goal by Chicago's Brandon Vincent. Julian Russell's attempted cross from the right side of the penalty area deflected off Vincent and bounced right past the goalkeeper Jorge Bava.
Atlanta poured in after halftime against the Fire (1-1-1), who played a man down most of the game after Johan Kappelhof was sent off in the 15th minute for dragging down Martinez as he was breaking toward the goal.
"The game very early started bad for us," Chicago coach Veljko Paunovic said.