Posh striker Conor Washington’s 10th goal of the season cancelled out Lauri Dalla Valle’s second goal in as many games for Alex, who have now won just one of their last eight matches.
Crewe took the lead after three minutes as former Peterborough player Nicky Ajose chipped a ball into the area to Dalla Valle and he spun near the penalty spot before firing the ball past goalkeeper Ben Alnwick.
The visitors conceded in the 66th minute when Marcus Maddison’s shot from 20 yards was parried by Paul Rachubka to Washington who fired home from inside the area.
The goal was Posh’s first in over eight hours of football and they were on the front foot again with Washington who went down under a challenge by George Ray inside the area, although no penalty was given.
Washington also saw a close-range shot saved but the draw means the hosts now appear certain to miss out on the play-offs.