Ryan Auger, who had begun the match on the right-hand side of midfield, completed 74 minutes in total in goal as a makeshift replacement for Chambers, who was injured as early as the fifth minute. The former Derby County and Arsenal shotstopper gamely continued until the 22nd minute, when the decision was taken to withdraw him to prevent further damage.
Blues managed to take the lead through in-form George Smith twelve minutes before the break, but their progress was further hindered ten minutes into the second half when Ofori-Acheampong was dismissed after an off-the-ball altercation with defender Ryan Cotton.
However, Ricky Duncan's men bounced back from this setback and Jacob Joyce's 72nd minute strike to forge ahead once again thanks to winger Julian Okai, only for Josh Capocci's late effort to earn Posh a share of the spoils.
Duncan was able to call on midfielder Alex Woodyard, who came into a side shorn of Michael Hyland (injury) and Hicham Abdellah (suspension). Auger took the wide-man's place, with the team otherwise unchanged. Michael Hassini continued to partner Louis Baucutt at the heart of defence with fellow Under-16s talent Dominic Iorfa having decided to accept Wolverhampton Wanderers' offer of a scholarship.
Peterborough began the game at a high-tempo and caused Southend all sorts of problems in the opening stages, with Chambers pulling off a miraculous save in the first minute to keep out Arthur Lee's fierce effort. Lee also prodded the rebound wide of the post after the 'keeper had parried the ball back into his path.
Three minutes later Kgosi Ntlhe thought that he had put Posh in front, but his effort from another Joe Newell corner was ruled out for a push and it was Chambers' efforts in attempting to keep the skipper's header out that led to his injury.
Auger had Blues' first effort on goal, flashing over from the edge of the penalty area in the eighth minute, and slowly the Shrimpers managed to break up the play. Having reverted to goalkeeping duties, Auger was rarely tested, and he gathered a weak Capocci shot from distance on the half-hour mark.
Southend took the lead after Okai had scrapped for the ball in midfield in the 33rd minute. It fell for Smith, who fed it back to his fellow second-year scholar and, despite the flanker's shot bouncing back off of the inside of the right-hand post, Smith was in place to slam the rebound into the roof of the net.
The half ended with James Stevens firing a free-kick over from the distance, and this was how the second period began as well, the Blues' captain this time directing his set-piece narrowly over.
Having done a good job of protecting Auger with some excellent defensive work as a team, the Shrimpers were further inconvenienced when Ofori-Acheampong was sent off after becoming involved in a scuffle with Cotton, the referee showing the red card for a head-butt on the centre-half.
Despite this, Southend continued to push on, and goalkeeper Alex Archer spilled Stevens' 30-yard piledriver, with a defender scurrying across to clear ahead of the onrushing Anthony Furlonge.
Midway through the second half, Auger made an outstanding stop at point blank range as Joyce headed Capocci's right-wing centre goalwards, the replacement custodian flying to his left-hand side to push the ball around the post.
Okai then set off on a marauding run, slashing over from distance, and Peterborough were soon level. Ben Seymour-Shove crafted the opportunity on the left, crossing for Joyce, who got ahead of Auger to tap into the net.
Incredibly, Southend responded immediately, with Smith - forced into a centre-forward role - combining well with Okai to help the 18-year-old score his eighth goal of the season. Okai began the move with a foraging run down the left, offloading to Smith before receiving the return pass from the byeline to slot into the bottom right-hand corner.
Ntlhe headed over for the shell-shocked hosts, who were thwarted again by Auger when the first-year leapt up to turn Newell's header over the crossbar nine minutes from the end.
The match was becoming increasingly stretched, and Smith slashed wide when a Stevens free-kick failed to drop kindly onto his right foot. Woodyard then drove goalwards from the goal-kick, Archer gathering besides his near post.
Hassini did a tremendous job in protecting Auger's goal by throwing himself at a fierce Ntlhe effort, but with less than two minutes remaining, Southend were denied a famous victory by Capocci. The midfielder picked up the ball on the right-hand edge of the penalty area and fired into the bottom left-hand corner, with the shot possibly taking a slight deflection on the way past Auger.
Even then Southend refused to lie down, and Baucutt's high cross was fumbled by Archer, with Okai and Furlonge unfortunate not to be able to connect with the loose ball as Posh cleared their lines during a tense six minutes of stoppage time.
Southend United: Luke Chambers (Fope Coker 22), Anthony Furlonge, Teddy Nesbitt, James Stevens, Michael Hassini, Louis Baucutt, Ryan Auger, Alex Woodyard (Jack Paxman 90+5), Duane Ofori-Acheampong, George Smith, Julian Okai. Substitutes not used: Lyle Della-Verde, Rhys Mackay.
Goals: Smith (33), Okai (73).
Cautioned: Furlonge (77 - foul tackle), Nesbitt (90+2 - delaying the restart of play).
Dismissed: Ofori-Acheampong (55 - violent conduct).
Thanks to the Shrimpers Trust website for the reprinting of these reports, for the Trust's own youth section, go here: www.shrimperstrust.co.uk/home.asp?page_id=10
