Magee then scored his 19th goal of the season tying the league lead with Montreal's Marco di Vaio in the 42nd minute when Alex's shot deflected off Magee's right shoulder.
Defender Jalil Anibaba put Chicago up 3-0 in the 52nd minute with his first goal of the season.
Dallas fought back with two second-half goals from Kenny Cooper, but the home defeat left the Texan club's campaign on the brink.
New England's Jose Goncalves scored the sole goal in the 31st minute, extending Montreal's winless streak to five games.
The Revolution's win was tarnished by the loss of forward Saer Sene to a broken leg in the 19th minute.
Philadelphia needed a 90th minute goal from substitute Jack McInerney to salvage a point at D.C. United.
The Washington club looked like recording only its fourth win of the season after taking the lead via a Nick DeLeon long-range swerver in the 36th minute and creating ample opportunities to score more.
However McInerney scored a rare goal when he headed in a Kleberson cross from close range.