Billy Jones scored twice as Crewe won for the fifth time in six games to ease their League One relegation fears.
On-loan Hereford keeper Peter Gulasci tipped Clayton Donaldson's thunderbolt onto the bar, and kept out headers from Calvin Zola and Chris McCready.
But he could not save Jones' penalty, awarded after Sam Hewson was sent off for handling on the line.
Toumani Diagouraga headed in a corner to level, but Jones smashed in a 30-yard screamer to earn a deserved win.
Crewe:
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Booked: Zola.
Goals: Jones 55 pen, 82.
Hereford:
Sent off: Hewson (55).
Goals: Diagouraga 79.
Att: 5,195
Ref: Kevin Friend (Leicestershire).
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