Hartlepool returned to winning ways with a stylish display at Orient.
Ian Moore raced clear to put Pools ahead by beating Stuart Nelson at the second attempt, before James Brown made it 2-0 from 25 yards.
Indecisive goalkeeping by Jan Budtz resulted in JJ Melligan halving Orient's arrears from outside the box.
Andy Monkhouse hammered in United's third, substitute Charlie Daniels pulled one back but Moore completed the scoring with a low drive.
Leyton Orient: Nelson, Terry (Demetriou 62), Thelwell, Mkandawire, Palmer, Melligan, Thornton, Chambers, Corden (Daniels 67), Gray (Echanomi 73), Boyd.
Subs Not Used: Morris, Oji.
Booked: Thornton, Mkandawire.
Goals: Melligan 57, Daniels 87.
Hartlepool: Budtz, McCunnie, Nelson, Antwi, Humphreys, Brown (Porter 73), Liddle, Boland (Clark 83), Monkhouse, Barker (Mackay 90), Moore.
Subs Not Used: Elliott, Lee-Barrett.
Booked: Monkhouse, Moore.
Goals: Moore 10, Brown 51, Monkhouse 84, Moore 90.
Ref: Mark Haywood (W Yorkshire).