Wizard wing-man Rodney Jack ran Mansfield ragged as four goals in 16 minutes sent Crewe to their first away win since March and condemned sorry Mansfield to their third successive defeat.
Jack scored one and made two goals as the Alex punished Mansfield's already leaky defence with three goals in eight first-half minutes.
The Stags failed to stem the tide in the second half and have now conceded 18 goals in their opening six games.
Afterwards dejected manager Stuart Watkiss said: "It was a shocking day, a shocking display and the players can have no excuse for a performance like that.
"If it hadn't have been for our goalkeeper (Kevin Pilkington) it could have been double figures."
Delighted Crewe boss Dario Gradi said: "It was our best performance of the season. We looked lively from the kick-off and all the players did well. Jack was the matchwinner, Mansfield just could not handle him."
Injury-hit Mansfield, who gave teenager defender Danny Holyoak a debut as a second-half substitute, were dealt a further blow when leading scorer Colin Larkin limped off after just eight minutes.
And by the 14th minute their patched-up side should have been three goals adrift. First Jack's close-range snapshot was tipped over by Pilkington's reflex save and then the unmarked Kenny Lunt blazed over from close range.
The Stags had a double let-off in the 14th minute. Another mazy run from Jack set up Colin Little and when his fierce shot was blocked by Pilkington, Jack somehow got in the way of Rob Hulse's follow up.
But there was no let-off on the half-hour as Crewe ran amok, scoring three goals in eight minutes. First Jack headed down David Vaughan's corner for Richard Walker to turn the ball in and then Jack raced onto Hulse's crossfield pass and out-paced Neil Moore before hammering in a 20-yard drive.
Two minutes later Jack again created havoc in the home defence and Hulse pounced to score from six yards.
Mansfield were restricted to long-range shots in the first half, substitute Iyseden Christie and Andy White both going close.
But there was no way back two minutes into the second half when Steve Foster headed in Lunt's free kick.
Lunt then completed Mansfield's misery with a fine, curling 20-yard free-kick in the 65th minute