The Liberian-born attacker scored an excellent goal to bring his side within two points on the Western Conference leader.
Dallas had a setback early in the first half. With just seven minutes gone, striker Eric Hassli pulled up lame. With Blas Perez on international duty and Kenny Cooper not in the squad due to a family emergency, the injury left the Hoops with a lack of attacking options. Je-Vaughn Watson replaced the big Swiss and pushed Fabian Castillo forward.
Darlington Nagbe opened the scoring with a sumptuous strike in the 53rd minute. George John did well to defend the forward, but Nagbe spun and lashed a shot into the upper corner of the far post, making a difficult goal look effortless.
Portland's lead could have been even more emphatic if not for the form of Dallas keeper Raul Fernandez. The Peruvian came up with a big goal-line save on Diego Chara in the 39th minute, before stopping a Diego Valeri volley in the 68th minute with a fantastic reflex save. He came up big again in the 75th minute, diving to his side to touch away a Diego Chara effort.
The result cuts Dallas' lead at the top of the West over third-placed Portland to two points.