In soggy and windy conditions Saturday night, Harrison Shipp opened the scoring with a sparkling finish and the Chicago Fire easily handled the Impact 3-0.
"The team performance tonight was poor. We weren't sharp," said Klopas. "Whether the field conditions played a part in it I don't know, but we could have done better."
"There were moments that we turned the ball over too many times and that turned into opportunities for them," he added.
Chicago snapped a four-game winless streak to improve to 4-5-2. Chicago's Jon Busch wasn't forced to make a save for his first shutout of the season and the 83rd of his MLS career.
Chicago broke out in the 13th minute. Kennedy Igboananike beat Bakary Soumare for a loose ball in the left corner and found Shipp streaking through the penalty area. Shipp made no mistake, using the left to bury it upper 90 for his second of the season and give the Fire the early lead.
Montreal went down a man in the 37th minute when Marco Donadel was shown his second yellow card of the match for a bad tackle and was excused.
"We were a bit slow to react in the middle and some of the matchups out wide were difficult," said Calum Mallace. "The red card, the penalty and the tough conditions made it a difficult game to play. It's difficult to get a starting eleven out there with all the injuries, but we have confidence in all the guys and we will keep grinding out until we get all guys healthy."
The Fire made it 2-0 at the 45 minute mark. David Accam deked Soumare on the edge of the 6-yard box and the defender hauled him down, drawing a penalty kick for Chicago. Jeff Larentowicz calmly fired to his right as Evan Bush dove the other way.
"We started off the game poorly and gave up the first goal early," said Bush. "After that, we got a red card and then a penalty. You get down 2-0 playing with 10 guys, you're hoping to keep it close and pull one back but we couldn't do that tonight."
Chicago added an insurance goal in the 72nd minute. Igboananike took a feed from Razvan Cocis in the midfield, outraced Soumare to the penalty area, and beat Bush cleanly for his first career MLS goal.
Montreal (2-4-2) had won its previous two matches.