The O’s are now eight points adrift at the foot of League Two.
All three goals came inside nine first-half minutes which only made a big task even more challenging for Danny Webb and his men.
James Collins broke the deadlock, before Joe McNerney and Enzio Boldewijn wrapped up the three points.
In what was an emotionally draining week for the east Londoners, following their High Court order and a near liquidation from a tax order, this defeat will leave a sour taste in the mouths of Orient fans.
It was another sorry afternoon for Orient and with seven games remaining, the O’s look certain for the drop.
Injury Crisis for Orient
It’s a fourth loss on the bounce for Leyton, who edged the opening exchanges of the match, and were unfortunate to lose Tom Parkes through injury early on.
Parkes, a huge figure for the O’s, was a notable miss as Crawley sprung what could be a defining 10 minutes for Orient and their survival hopes as Collins slotted home the first goal on the day.
Five minutes later Crawley made it 2-0, as Joe McNerney headed past Orient keeper Sam Sargeant following another set-piece.
Orient were dejected. It was a fantastic second goal for Crawley and for Webb’s men it was always going to be an uphill task from then on.
But unfortunately for Leyton Orient it got worse. Shortly after the second goal, Boldewijin’s header was adjudged to have crossed the line and Crawley were 3-0 ahead.
With the contest and the three points essentially sorted, Orient’s youngsters didn’t give up.
The front three of Liam Kelly, Steven Alzate and Josh Korma tried breaking Crawley down on the counter but failed to be clinical.
Deep into stoppage time, Orient were denied a clear penalty when Alzate was fouled within the penalty area but it was quickly forgotten about when referee, Trevor Ketttle blew his whistle.
It was a day for Orient fans to forget and unfortunately for them it could be a day they remember, as the day the dream of staying in League Two ended.
CRAWLEY TOWN: Morris, Young, Yorwerth, McNerney, Boldewijn (Cox 79), Smith, Payne Blackman (Lelan 73), Djalo (Clifford 57), Collins, Murphy.
SUBSTITUTES: Mersin, Harrold, Bawling, Henderson.
GOALS: Collins (23), McNerney (29), Boldewijn (32).
LEYTON ORIENT: Sargeant, Judd, Hunt, Parkes (Mezague 12), Kennedy, Alzate, Atangana (Ochieng 81), Kelly, Semedo, Koroma (Liburd 62), Massey.
SUBSTITUTES: Grainger, Clark, Moncur, Abrahams.
BOOKED: Kelly (28)
REFEREE: Trevor Kettle
ATTENDANCE: 2,918 (792 Orient fans)