Bonfigli, who entered the game in the 69th minute as a substitute for Paulo Junior, was playing in only his second MLS game and played only one minute in his previous appearance. Will Johnson set up the score with a pass that went between two FC Dallas defenders to Bonfigli, who raced past defender George John and scored from about 15 yards away.
Real Salt Lake (5-3-1) snapped a two-game losing streak.
Brek Shea scored on a controversial penalty kick in first half stoppage time for FC Dallas (3-3-2), which remained unbeaten at home at 3-0-2. The penalty kick was awarded after Tony Beltran was called for a handball inside the penalty area. Replays showed the ball went under Beltran's arm.
Real Salt Lake is now 0-10-2 all-time in Dallas.
RSL will next host Toronto FC Saturday night at Rio Tinto Stadium. The game can be seen on CW30 beginning at 7:00 p.m.