Erhun Oztumer scored a superb free-kick as Peterborough United clung on with 10-men to secure a vital win at Leyton Orient.
The home side made a bright start to the encounter and almost found themselves in front inside the opening two minutes as Jobi McAnuff outpaced Bostwick down the left and crossed for Cox, whose shot was cleared off the line by Ntlhe.
The deadlock was broke rather against the run of play on eight minutes as a glorious cross from Joe Newell was guided past Legzdins by Aaron MCLEAN who notched his first goal since returning to the club on-loan from Bradford City.
On 17 minutes, Dean Cox, who had made a lively start, curled a free-kick over the crossbar after Zakuani felled Batt off the ball.
Oztumer was cautioned for throwing the ball away on 35 minutes by the referee who had earlier booked Scott Cuthbert for a foul on Mackail-Smith.
The home side were level on 38 minutes and it can be put in the soft goal to concede category for Darren Ferguson's men. A low cross from Cox was not a danger until it was hooked into the path of BATT by Pritchard and the former Posh loanee drilled low past Alnwick.
On 43 minutes, Harry Beautyman had a great opportunity to score on his return to his former club, but volleyed wide after Legzdins spilled a routine cross from Ntlhe.
Two minutes after the re-start, Posh were in front and what a goal it was. Mclean was felled on the edge of the box and up stepped Erhun OZTUMER to curl home a delightful free-kick over the wall and into the back of the net.
The hosts made a change just after the hour mark with Jay Simpson replacing Batt in attack.
Newell was booked for a tug back on Vincelot in the centre circle. Oztumer curled a free-kick over the bar on 74 minutes after Mclean was felled.
Alnwick denied Wright with his legs as the former Posh trialist let fly from 25-yards on 85 minutes. Newell was given a second yellow card as the game moved deep into stoppage time for a foul.
In the seventh minute of added time, Posh withstood an almighty scramble as Ntlhe cleared off the line before Alnwick pounced on a loose ball to joyous scenes in the Posh dugout.
Leyton Orient: Legzdins, Sawyer, Vincelot, Cuthbert, Cox, McAnuff (sub Adeboyejo. 82min), Lowry, Batt (sub Simpson 61min), Clarke, Wright, Pritchard. Unused subs: Baudry, Lee, Omozusi, Kashket, Woods,
Posh: Alnwick, Bostwick, Zakuani, Burgess, Ntlhe, Payne, Beautyman (sub Anderson 83min), Newell, Oztumer, Mackail-Smith, Mclean. Unused subs: Day, Smith, Mendez-Laing, James, Washington, Vassell.
Half-time: Leyton Orient 1-1 Peterborough United
Attendance: 5,546 (916 Posh).