Only six minutes had passed when James Walker curled a shot around home keeper Sam Cole and into the net.
Dominic Green grazed the top of the crossbar for Posh before Adetayo Osifuwa might have done better when a free-kick found him unmarked six yards out, but his header went wide.
Josh Simpson's volley came closest to an equaliser though Damien Scannell did his best to increase Southend's lead, first with a shot just past the post, then a goalbound effort was deflected wide.
Duran Reynolds also headed wide just before a half hour that saw two goals in two minutes and the game lost.
On 31 minutes Jamie Day scored direct from a free-kick which went over the the wall and the dive of Ian Joyce.
On 33 Green at last found the net, an earlier free-kick had gone over the bar soon after hitting it, with a low shot giving Joyce no chance.
Asante was denied by good work from Cole but it was Krystian Pearce for Posh who should have made the game safe when he missed a sitter from close in.
Simpson had two shots well saved by Joyce, in-between Batt shooting wide and Wright missing yet another great chance.
There was some respite for the hard working Blues defence when good work from Craig Calver saw a Walker effort well blocked, and Walker then hit the crossbar with a superb free kick.
So, in a game of free-kicks going in, or close, it was no surprise when up stepped Stuart O'Keefe in the 92nd minute to curl another cracker over the Posh wall and into the net for an entertaining game to finish all square.
Southend United: Joyce, Owinja, Osifuwa, James-Lewis, Reynolds, Whittikar, Scannell, O'Keefe, Calver, Asante (Crawford 75), Walker.
Unused subs: Bentley, Dennis, Milner.
Peterborough United: Cole, Piergianni, Martin (Austin h-t), Day, Dove (Davies 55), Pearce, Simpson, McCrae, Wright, Batt, Green.
Unused subs: Adjei, Ralph, Lee.