Club Deportivo Chivas USA were unable to capitalise on home advantage as a stoppage-time winner saw them slip to a 2-1 defeat to Chicago Fire.
Juan Pablo Angel opened the scoring for the home side from the penalty spot after 23 minutes.
Austin Berry had brought down Alejandro Moreno inside the area, but then atoned for his error by scoring the equaliser just two minutes later.
The teams went into the break on level pegging, but it was the visitors who took the initiative after the restart and dominated the second half.
Sebastian Grazzini saw his 62nd-minute effort saved by Dan Kennedy before Arne Friedrich looked to have blown the chance for Chicago to win in the 92nd minute.
The German international rose highest to meet Marco Pappa's cross but flashed his header high and wide.
The decisive moment came when Frederico Puppo supplied Pappa on the edge of the area and the Guatemalan struck home the winner as the seconds ticked away.
