Canadian striker Marcus Haber proved the hero for Crewe as he slotted home the winner from the penalty spot shortly after the half-hour mark.
Michael Bostwick was adjudged to have hauled down Adam Dugdale inside the area and denied a goalscoring opportunity following a Crewe corner.
Bostwick was dismissed for the foul, with Haber putting the hosts ahead at Gresty Road, before Jack Baldwin's red card capped off a poor night for the high-flying visitors late on.
Crewe's third win on the bounce moves them into 22nd, with 10-man Scunthorpe United the only other side in the bottom four to pick up a point - Lyle Taylor gaining Mark Robins' men a 2-2 draw at Port Vale, despite Jennison Myrie-Williams' second-half dismissal for a second yellow card.
Fellow strugglers Yeovil Town and Walsall were beaten 2-0 by Sheffield United and 1-0 at Crawley Town respectively, while Bristol City maintained their unbeaten run at the summit.
Despite being held to a 2-2 draw by Bradford City at Ashton Gate, Steve Cotterill's side were able to extend their lead at the top to six points thanks to Crewe's heroics against second-placed Peterborough.
Billy Clarke and Christopher Routis twice cancelled out goals from Aden Flint - with close-season signing Routis' first Bradford goal coming five minutes from time to ensure a point.
Preston North End closed the gap on Peterborough to a point with their fifth win in a row, as Paul Gallagher continued his fine goalscoring run to ensure maximum points in a 1-0 win at Gillingham.
The former Blackburn Rovers and Leicester City man has now scored in his last four games for Preston and the Scot's winner was all the more valuable given results for their play-off rivals.
Kyle McFadzean and on-loan Arsenal striker Benik Afobe helped MK Dons come from behind to win 2-1 against Fleetwood Town, while Notts County went one better as they recovered from a two-goal deficit to see off Barnsley 3-2 at Oakwell.
Garry Thompson got the comeback started after 20 minutes before Michael Petrasso's brace completed the turnaround.
Swindon Town slipped out of the play-off places thanks to Bastien Hery's late winner in a 3-2 success for Rochdale, while Coventry City's miserable run continued with a 4-1 reverse at Oldham Athletic.
Jay Simpson and Darius Henderson scored in either half as Leyton Orient saw off Doncaster Rovers 2-0, with Colchester United coming from a goal down to beat Chesterfield 2-1.
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