Robert Beric's goal near the end of the first half proved to be the only score of the evening as the host Chicago Fire FC imperiled Real Salt Lake's playoff chances with a 1-0 win on Saturday night.
Playing its final home match of the regular season, the Fire (9-16-7, 34 points) extended its unbeaten streak to three, while RSL (12-12-6, 42 points) lost for the eighth time in its last nine matches on the road.
The defeat left RSL in eighth place in the Western Conference, a point behind Vancouver for the seventh and final playoff spot with just four matches left in the regular season.
Chicago controlled the offensive pace for much of the first half, with three of its 11 shots on goal, including a Beric shot that was saved by RSL netminder David Ochoa in the 38th minute.
However, Beric made the most of his next opportunity when his shot on the right corner found its way past Ochoa to give the Fire a 1-0 lead in the 45th minute. It was his eighth goal of the season and third in his last two matches.
The goal was assisted by midfielder Miguel Angel Navarro, his second of the season.
RSL, held without a shot on goal in the first half, made its best effort in the 71st minute when Albert Rusnak's shot from the center was stopped by Fire netminder Gabriel Slonina.
Anderson Julio's bid at an equalizer in the 76th minute sailed to the right.
Real Salt Lake's last chance at tying the match came when Justin Meram's shot was denied in the 88th minute. Chicago spent much of the remainder of the match -- which included five minutes of extra time -- on the offensive as RSL's desperate attempts to get the ball out of its zone proved unsuccessful.