Aaron McLean gave the visitors the lead with 16 minutes played, before Wayne Routledge netted an equaliser 11 minutes before the interval, leaving the Posh still searching for their first league win of the season.
The R's were first to threaten with Adel Taarabt firing straight at visiting keeper Joe Lewis, but it was the visitors who struck first.
Tommy Williams drifted in a cross and McLean was in the right place to head home his third goal of the season.
The Posh then pushed on for a second goal, but they were rocked back by an equaliser just past the half-hour mark.
Taarabt fed Jay Simpson and his cut-back left Routledge with the simple task of slotting home from close range, recording his fifth goal of the campaign, but his first in the league.
The second half was a relatively quiet affair until the closing minutes, when Simpson wasted a fine chance to give the home side victory.
However, right at the death, Rangers were grateful for the referee's assistant's offside flag which denied Craig Mackail-Smith of what would have been the winning goal.
There was still time for Simpson to head over when well-placed before the final whistle went and the points were shared.