Substitute Adelakun’s looping effort from a tight angle sailed into the net to deny Colchester a precious win.
Scunthorpe goalkeeper Luke Daniels denied Richard Brindley midway through the first half, while Gavin Massey headed Jacob Murphy’s cross wide with only Daniels to beat.
But Scunthorpe took the lead on the half-hour mark through Theo Robinson, who curled a delightful shot into the far top corner after the Colchester defence had failed to deal with Daniels’ long kick.
Colchester went close to equalising midway through the second half when Massey’s fierce effort was tipped on to the crossbar by Daniels.
Tom Eastman equalised for Colchester with nine minutes remaining when he slammed home from six yards after Scunthorpe had failed to clear Massey’s corner.
Colchester went ahead four minutes later through Chris Porter, who latched on to David Fox’s pass and wriggled past Marcus Williams before firing past Daniels, but Adelakun broke Colchester hearts with a late equaliser.