Captain Luke Chambers rescued a point for Ipswich Town as he headed home deep in stoppage time at London Road.
Paul Lambert's men had been heading to defeat despite taking an early lead against their winless hosts, before the skipper met the ball to head home a corner for which giant goalkeeper Tomas Holy had come up to contest.
James Norwood opened his Town account after just four minutes as he profited from an error from home keeper Christy Pym, but the visitors were pegged back before the break by Ivan Toney's header before Mo Eisa's neat finish secured three points for Darren Ferguson's men.
Norwood missed a golden chance to equalise as he saw a penalty saved by Pym, after Kayden Jackson was brought down, and that was as close as Town came to forcing an equaliser.
That is before Chambers intervened to earn a point, with Lambert racing onto the pitch to celebrate the goal.
In truth the Blues were perhaps second best in this game, as they struggled to exert themselves on their hosts and work the ball through the thirds, with Peterborough looking the more likely to add to their lead in the closing stages rather than Ipswich finding a leveller.
That means Town, who were well-backed by more than 4,000 away fans this afternoon, have taken five points from a possible nine at the start of their League One season, heading into Tuesday night's home clash with AFC Wimbledon.
Paul Lambert made just one change to the side which started the Blues' last league game, at home to Sunderland a week ago, with Gwion Edwards returning to the starting line-up in place of injury victim Luke Garbutt.
And, after a frenzied few minutes of congested midfield play, the visitors were ahead.
It started down the left flank as the ball was worked back to Myles Kenlock who launched a diagonal ball into the box which home keeper Christy Pym was heavy favourite for. However, the former Exeter man got caught under the ball under pressure from Norwood and Posh defender Mark Beevers, before the Town striker profited on a loose ball to fire home.
Flynn Downes fired over the top and Danny Rowe had an effort saved by Pym before the visitors came into the game, with Marcus Maddison having an effort over from the edge of the penalty area following George Boyd's cross.
The hosts should have been level on 23 minutes, when Toney's firm header was straight at Tomas Holy before Edwards had a shot saved, but the home side didn't have to wait too much longer for parity.
Luke Woolfenden gave away a free kick down the right as he gave the referee a decision to make when tangling with Toney, and the striker was able to escape Donacien from the resulting set-piece to head his side level.
Holy needed to react quickly to catch Maddison's effort from halfway before the first period came to an end and was in the thick of things early in the second period as saved superbly from Maddison and then Mo Eisa as he palmed the second effort out of danger.
The Blues were on the front foot again soon, though, with Cole Skuse having an effort palmed away by Pym before Edwards shot through traffic but straight down the goalkeeper's throat.
In truth Peterborough's second had been coming long before Chambers' outstretched leg could only divert the ball into the path of Eisa to finish as London Road let out an almighty roar.
The roar was soon coming from the 4,000 traveling Town fans after Jackson was brought down by Frankie Kent in the box, but Norwood's penalty was poor and easily saved by Pym as a big chance went missing.
Peterborough tails were up but the home crowd was silenced when Chambers headed home.
Peterborough: Pym, Blake-Tracey, Kent, Beevers, Mason; Reed, Knight, Maddison (Tasdemir 74), Boyd; Toney, Eisa (Ward 85)
Subs: O'Malley, Butler, Burrows, Kanu, Dembele
Ipswich Town: Holy; Donacien, Chambers, Woolfenden, Kenlock; Rowe (El Mizouni 74), Skuse, Downes, Edwards (Judge 66); Jackson, Norwood
Subs: Holy, Wilson, Huws, Dozzell, Roberts
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