Garry Thompson struck late in the half to cancel out Marc Maddison's opener as Notts County and Peterborough United went into the break level at Meadow Lane.
Maddison gave the visitors the lead when his long-range effort took a deflection off Hayden Mullins to wrong-foot goalkeeper Roy Carroll on 13 minutes.
Posh were looking for a penalty shortly after when Conor Washington went down under a challenge in the area, but the official waved away the appeals.
The home side started to get the better of proceedings after the half-hour mark, with Balint Bajner particularly involved.
The Hungarian striker's best chance arrived when he forced Scott Loach into a good save after beating his man to open up room for the shot.
With the first half petering out, Thompson made the most of some space to fire a powerful equaliser home.
