A deflected strike got the Iron ahead in a first half that Scunthorpe dominated, but could not extend their lead further until the second half.
Paddy Madden netted for the Iron after the break, with a powerful effort from close range, and the hosts survived a late scare after Izale McLeod’s goal to claim a vital victory.
The win helps to lift the Iron away from their visitors and goes a long way to helping them to securing League One football at Glanford Park next season.
Mark Robins made two changes to his side going into the game, welcoming back Niall Canavan and Neal Bishop, with both returning from respective injuries.
Bishop came back to captain the side, recovering from a hernia operation sooner than expected and meaning that he could play a part in the Iron’s crucial end of season run in.
Crawley headed to Glanford Park in good form though, having climbed out of the bottom four after a run of three wins in their last five.
They have been boosted by the goals of Izale McLeod, who has netted 18 times this season and led his side out for the trip to Glanford Park.
It was the Iron who started the game the brighter as good play from Paddy Madden on the right hand side ended in Jordan Clarke’s shot blocked on the line.
The Iron were getting a lot of joy down the flanks in the early exchanges, and Theo Robinson’s cross nearly created a chance for Kevin van Veen, but veteran ‘keeper Brian Jensen claimed it at the second attempt.
The visitors had been on the back foot for most of the opening quarter, but soon sprung into life after an excellent passing move, eventually forcing Luke Daniels to tip an Izale McLeod drive over his crossbar.
That was a rare glimpse of goal for the prolific striker, who was excellently marshalled by the returning Canavan and fellow centre back Alex Davey.
The Iron soon took advantage of their bright star and took a 19th minute lead through Jordan Clarke’s deflected strike from just inside the area.
Gary McSheffrey did well on the Iron’s right hand side, before cutting it back for Clarke, whose effort went in off Crawley defender Ryan Dickson.
Mark Robins’ side did not rest on their one goal advantage and pushed forward in search of a second, although McSheffrey’s long range drive was gathered by Jensen.
The Iron were dominant, but could not manage to find a second goal that would have capped an excellent first half, while Lee Fowler’s ambitious free-kick was as close as the visitors came.
The second half began as the first had ended, with the Iron continuing to trouble visiting ‘keeper Jensen, who had to be alert on more than one occasion.
The ‘keeper stood firm to deny a fiercely struck Madden effort and was also at full stretch to deny van Veen, as the Dutchman tried his luck from the corner of the box.
The pressure showed no sign of ending, with Isaiah Osbourne dispossessing Gavin Tomlin before unleashing a powerful drive, which Jensen could only beat away.
Crawley had a couple of dangerous set pieces, but the Iron dealt with everything that the Red Devils were throwing at them and limited service to the dangerous McLeod.
Just after the hour mark, the Iron looked to have put the game beyond doubt as Madden drilled into the top corner from close range.
A dangerous ball into the box was flicked on by Canavan, who found Madden lurking at the back post to fire past Jensen.
The Iron nearly made it three just minutes later, but the influential McSheffrey saw his effort tipped around the post, following a great lay-off from Theo Robinson.
Crawley boss Dean Saunders made a few changes to try and get his side back into the game, and they got a lifeline thanks to McLeod’s effort.
The visitors put a good move together down their right flank and the striker swept home Lewis Young’s cross to give Crawley a chance with 15 minutes still to play.
The Iron did not sit back and try to hold onto what they had got, with second half substitute Hakeeb Adelakun close to adding a third, although he could not lift his effort over Jensen.
Crawley tried to mount a late spell of pressure, but did not really trouble Luke Daniels in the Iron goal, with the ‘keeper able to claim most things comfortably.
The Iron were resolute as they looked to see the game out in the final moments and could even have extended their lead as the match drew to a close.
Scunthorpe United: Daniels, Clarke, Davey (Boyce, 46), Canavan, Williams, Bishop, Osbourne, McSheffrey (Lundstram, 82), Madden, van Veen, Robinson (Adelakun, 70).
Substitutes: Anyon, Townsend, Evans, Syers.
Crawley Town: Jensen, Oyebanjo, Dickson (Edwards, 69), Bradley, McLeod, Morgan, Young (Harrold, 87), Fowler, Tomlin, Youga, Elliott (Pogba, 73).
Substitutes: Price, Smith, Bawling, Cofie.
Attendance: 3,009 (102 away).