Boss Darren Ferguson admitted Peterborough's poor home form could cost them dear.
Ferguson watched the npower Championship strugglers fail to win for 13th time in 18 games at London Road although they were grateful for a point as Michael Bostwick's 71st-minute equaliser rescued a 2-2 draw against Charlton.
The disappointing result saw them fall to two points from safety and it was not the start to a crunch week that Ferguson wanted.
Ferguson said: "In our situation any match we fail to win goes down as a missed opportunity - that's certainly the case. We failed to take some fantastic chances to get a second goal after going in front and then we were all over the place after Charlton came back at us.
"We got ourselves together again to equalise and could have nicked a win at the end, but our home form hasn't been anywhere near the level we expect all season and that is clearly an issue we need to address.
"I viewed this week, with Charlton at home and Ipswich coming here on Saturday, as a great chance to put six points on the board. The most we can get now is four and that makes Saturday the biggest game of our season. it is a must-win if we are serious about staying up."
Posh broke the deadlock just past the mid-point of the opening period when Danny Swanson notched a delightful first goal for the club. But Charlton skipper Johnnie Jackson levelled when bursting onto a Callum Harriott pass and firing across goalkeeper Bobby Olejnik in the 55th minute.
And that was swiftly followed by a second from hitman Danny Haynes, who pounced after Olejnik had clawed out a Michael Morrison header. Posh refused to roll over and Bostwick restored parity when his bouncing long-range blast deceived the diving Button, but the Charlton keeper redeemed himself when blocking a stoppage time header from Tommy Rowe as the hosts searched for a winner to no avail.
"I think a point apiece was about right overall," said Charlton boss Chris Powell. "We started well only to find ourselves behind, but then responded very well in the second half to get in front.
"Both teams had chances and both could have won it, but I'll settle for a point after a couple of poor results lately. We're only six points clear of the relegation zone so we can't afford to be complacent. That sort of gap can be wiped out very quickly so and we must continue to work hard."