Ashley Westwood and Clayton Donaldson scored second-half goals as 10-man Crew saw off battling Grimsby 4-2.
The home side cold have been out of sight after half an hour but Donaldson and Shaun Miller were thwarted by a string of saves from Nick Colgan.
The Alex took the lead in the 29th minute when Joel Grant nodded down Westwood's centre and Byron Moore swept home from 12 yards.
The lead lasted just three minutes as Jean-Louis Akpa Akpro shot between defenders John Brayford and Danny O'Donnell and fired into the far corner of the net, before two minutes later, Moore returned the favour to set-up Grant for a precise side-footed finish.
But the Mariners were level again four minutes before the break. Brayford's loose headed clearance fell to Nick Hegarty who picked out Dean Sinclair to net from six yards.
Ten minutes after the break Donaldson's cut-back found Westwood 25 yards out and the midfielder drilled a stunning first-time finish into the roof of the net.
Steve Phillips pulled off a stunning save from Lee Peacock's close-range header to keep the Alex in front and Carl Martin was harshly sent off for a late challenge on Michael Leary before Donaldson put the result beyond doubt with a solo effort at the death.
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