Peterborough United suffered their second successive league defeat as Leyton Orient continued their excellent form with a polished display at London Road as Dean Cox and a brace from the superb Mooney secured the points for the O's.
A corner kick from Grant McCann was headed across at the far post by Bostwick on six minutes, but Tyrone Barnett couldn't force the ball home with goalkeeper Jones managed to scoop the ball clear.
Lloyd James fired a low free-kick into the wall on 16 minutes after Assombalonga had been penalised for a foul 25-yards from goal.
On 24 minutes, a poor header from McCann fell invitingly for Cox, but he couldn't keep his volley down.
A minute later, Posh were in front as a low free-kick from McCann caused panic in the Orient defence, it appeared to strike ROWE and Barnett before rolling over the line, but the Posh skipper claimed it.
A stunning volley from Mooney struck the underside of the crossbar on the half hour mark before Cox and Cuthbert both went close with the latter denied by goalkeeper Olejnik.
The visitors levelled on 38 minutes as a ball into the box was collected by MOONEY and he spun and fired high past Olejnik and into the back of the net.
Moments later, Kevin Lisbie had a glorious chance to put the visitors in front, but he headed straight at Olejnik from close-range.
On the stroke of half-time, Swanson was denied by a fine save from Jones after good work in the build-up from McCann and Barnett.
McCann fired over two minutes after the re-start as Posh tried to get themselves back in front. On 49 minutes, Orient got their noses in front for the first time in the afternoon as hesitation at the back involving Olejnik and Bostwick allowed COX to nip and lob the ball into the unguarded net.
Olejnik somehow kept out Mooney with his legs as Orient came close to adding a third during a stretched opening to the second period.
On 58 minutes, the visitors made it 3-1 as MOONEY was left in acres of space on the right and he drilled home an angled drive into the bottom corner.
Joe Newell replaced Swanson on 65 minutes before Cox was denied by a fine save from Olejnik diving to his right. Olejnik denied a Mooney toe-poke on 73 minutes.
McCann fired a left-footed free kick wide on 79 minutes after substitute Jeffers had been felled on the edge of the box.
Final Score: Posh 1-3 Leyton Orient
Posh: Olejnik, Ntlhe (sub Mendez-Laing 53min), Zakuani, Bostwick, Swanson (sub Newell 65min), Payne, Assombalonga (sub Jeffers 78min), McCann, Rowe, Barnett, Little. Unused subs: Day, Brisley, Alcock, Conlon.
Leyton Orient: Jones, Omuzusi, Sawyer, Vincelot, Cuthbert, Cox (sub Batt 77min), James, Lisbie, Mooney, Odubajo (sub Bartley 90min), Clarke. Subs: Sutherland, Stockley, Gorman, Lasimant, , Larkins.
Attendance: 10,026 (1,666 Orient fans)