With less than a minute left in regulation, receiver Charles McClain ran the ball two yards for a touchdown to bring the Washington Valor within one point of the Soul.
But, with 42 seconds remaining, the Valor fumbled the extra point attempt and the Soul were able to hold on for a 48-47 road win.
Trailing 42-28 heading into the fourth quarter, the Valor made a late push, outscoring the Soul 19-7.
Quarterback Sean Brackett threw touchdown passes on Washington's next two possessions, the first a nine-yard reception by Greg Carr and the second a 13-yard catch by Josh Reese, to cut the Soul's lead down to seven.
But an 11-yard touchdown pass from Soul quarterback Dan Raudabaugh to receiver Darius Reynolds, and two failed extra point attempts on the Valor's last two scores were enough to keep the Soul undefeated at 7-0.
Raudabaugh completed 10 of 22 passes for 148 yards and five touchdowns. Receiver Ryan McDaniel caught two of them on four receptions for 54 yards, with the first being the 100th touchdown of his career on the Soul's opening possession.
Reynolds caught three passes for 54 yards and two touchdowns, and receiver Shaun Kauleinamoku made three receptions for 45 yards and a touchdown.
Sean Brackett completed 26 of 44 passes for 231 yards and five touchdowns, and Carr led Washington receivers with 12 receptions for 131 yards and four touchdowns to allow the Valor to keep pace.