Crawley captain Gary Alexander was the architect in the defeat with a goal in each half and former Iron striker Jonathan Forte came off the bench to rub further salts into the wound with Crawley’s third.
Scunthorpe, outplayed for long periods, created several clear-cut opportunities of their own but were guilty of poor finishing and ended the match with 10 men after midfielder Mark Duffy was dismissed with time running out.
The Iron went into the game unchanged from Tuesday night's heroic penalty shoot-out victory over Derby County but were soon under the cosh against a bright looking home side.
Alexander shot over in the first minute before forcing keeper Sam Slocombe to save his goal-bound header from a cross by Josh Simpson.
Billy Clarke then nearly put the home side ahead but his rasping low drive came back off the post with Slocombe well beaten and Alexander was unable to turn home the follow-up.
The deadlock was eventually broken after 33 minutes when a free-kick by Adams was missed by Slocombe and Hope Akpan headed back across goal to Alexander who could not miss from two yards.
The Iron grew into the game after the goal and should have headed into the break level when David Mirfin shot wide at the far post with the goal gaping following a corner from Josh Walker.
The second half started in lacklustre fashion and chances were hard to come by with both sides clearly feeling the effects of the blistering 30 degrees heat plus their respective cup triumphs during the week.
The home side made the points safe on 60 minutes when Tom Newey was ruled to have bundled over Alexander in the box. The experienced striker stepped up to send Slocombe the wrong way.
Substitute Forte, making his debut after joining from Southampton on Friday, sealed Crawley’s victory 10 minutes from time taking advantage of some hesitant Scunthorpe defending to head home past on-rushing keeper Slocombe.
The afternoon was soured further for the away side when Mark Duffy received his second yellow card of the game in the 86th minute for persistent fouling to round off an entirely depressing start to the season for Alan Knill’s men.