Yet another goal from Mike Magee helped the Fire overcome Toronto 1-0 to be fourth in the Eastern Conference.
Magee's classy chipped penalty on 64 minutes – his 20th goal of the campaign – gave Chicago a crucial three points.
Chicago's win came as the Portland Timbers maintained their one-point lead atop the Western Conference after a 0-0 draw at home to second-placed Real Salt Lake.
The Montreal Impact finally returned to winning ways in the league to move into third in the east with a 2-1 win at home to the Philadelphia Union.
Fabinho had put the Union, also chasing a play-off spot, ahead on 29 minutes before Montreal scored twice in the second half.
Marco Di Vaio's 20th goal of the season levelled things up before Karl Ouimette netted an 84th-minute winner, ending the Impact's six-game winless league run.
The loss leaves Philadelphia two points behind fifth-placed New England.
The Revolution also claimed a vital victory as they battled past the Columbus Crew with a 3-2 win at Gillette Stadium.
Teenage Uruguayan attacker Diego Fagundez struck the winner on 76 minutes after Columbus had twice levelled.
The Seattle Sounders' poor form continued and their play-off place is under threat after a 2-0 loss at Dallas.
Matt Hedges and Michel struck in the second half as Dallas condemned the Sounders to their fourth straight league loss.
Seattle are fifth in the Western Conference, four points ahead of San Jose with the Earthquakes holding a game in hand late in the season.
The Colorado Rapids jumped into fourth in the west as Gabriel Torres' brace led them to a 3-2 win over the Vancouver Whitecaps.
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