The Vancouver Whitecaps went 298 minutes without allowing a goal before a dreadful stretch emphatically ended that run.
The Chicago Fire are suddenly searching for offense after failing to score in two straight games for the first time.
The Fire will be looking for their first victory over the Whitecaps, who will conclude a five-game road stretch Saturday night.
Vancouver (8-5-6) had not allowed a goal since the first half of a 3-0 defeat at Los Angeles on June 23 before all the scoring occurred Wednesday in a wild second half of a 3-2 loss to Toronto.
Rookie Darren Mattocks gave the Whitecaps the lead in the 50th minute with the first of his two goals. But the normally steady defense collapsed, allowing Terry Dunfield's game-winner in the fifth minute of stoppage time.
"The hard lesson learned is that guys need to be more responsible for their jobs not just for 90 minutes but for 90 minutes plus," defender Jay DeMerit said. "If we can take that attitude into our game on Saturday, we can try to get a different result."
Chicago (8-6-4) saw a 3-0-1 stretch end with Sunday's 2-0 home loss to Los Angeles. The Fire had no shots on goal in the first half and finished with three.
"It's one game," coach Frank Klopas said. "We didn't lose anything right now. There's a lot of games to be played and we have to move on."
Vancouver posted a win and a draw against Chicago last year as an expansion team. This is the lone 2012 meeting between the clubs.
Fire goalkeeper Sean Johnson did not play in these teams' scoreless draw at Toyota Park on May 7, 2011, and he matched a career high by giving up four goals in a 4-2 road loss Aug. 7.
Johnson is anxious for the chance to see Chicago bounce back.
"I think a loss is gonna kinda spark a little fire under us," Johnson said. "We had a good four-game stretch. I think it's going to be a test for us to come out with a bit more intensity this game and a bit more bite."
Although the Fire will be the more rested club with the Whitecaps having just played three days earlier, Chicago doesn't believe that will be a major advantage.
"We don't want to think about that, thinking that they may be down or a little bit tired," defender Austin Berry said. "We definitely want to step up being at home and maybe put them under pressure."
Vancouver coach Martin Rennie will have striker Eric Hassli back from suspension. Hassli, though, may not start after Mattocks took his place Wednesday and moved into the team lead with six goals.
"He is a fantastic young player and he can be a star if he keeps working hard," Rennie said. "He has that finishing touch with that pace and movement. There are teams that fear playing against him and I think he is going to be an excellent player."
Vancouver's Joe Cannon continues to lead MLS with eight shutouts.