Striker Sharp was a constant thorn in the Oldham rearguard while veteran Peter Beagrie demonstrated all his skills, particularly in the second half to bamboozle the Latics defence.
Oldham looked quite bright in the opening half but once they lost the services of Chris Porter at half time they seemed to lose pace and poor defensive work led to their downfall.
There was a steady start with Marc Tierney and Paul Warne getting in testing shots against Paul Musselwhite, while Andy Keogh was wide of the mark for the Iron.
Oldham broke the deadlock in the 17th minute when lively skipper Andy Liddell drove in a free-kick from the left that curled low into the net from 25 yards.
Scunthorpe's response was immediate with a Butler header flying wide before the defender notched his first goal of the season in the 28th minute.
The goal was initiated by a Beagrie free-kick on the left which Keogh headed goalwards for Chris Day to block.
Crosby and Sharp saw their efforts also stopped before Butler came in to knock the ball home.
Three minutes later Scunthorpe grabbed the lead. Beagrie was again the architect with a ball from the left to the far post, Peter Till laid it back for Keogh but the ball fell to Sharp who rifled home with his right foot.
However, Oldham were quickly back on level terms. David Eyres hoisted in a free-kick from the right and a static home defence allowed Liddell to steer home a 33rd minute equaliser.
Musselwhite kept Scunthorpe in the game with a great save from substitute Luke Beckett in the 49th minute and that seemed to signal a change in the game.
The Iron began to assert themselves and after Day had brilliantly pushed the ball over from Sharp, Beagrie's left-wing corner reached the far post where skipper Crosby crashed home a 52nd minute left-foot shot.
Two minutes later the home side established a two-goal lead when Sharp grabbed his 12th goal of the season following excellent work by Keogh and Cleveland Taylor.
The young striker then missed a sitter while Oldham's nearest effort saw Marcus Williams head off the line from Beckett.