Substitute David Hutton earned the League One basement side a surprise draw at London Road with a 66th-minute strike following a howler from Posh goalkeeper Joe Lewis.
Allen said: "We performed with a lot of energy and commitment in tough conditions and came out of the game with a very good result.
"It's really hard for teams at the top at this stage of the season. You will see sides chasing promotion all around the country stuttering and that's what happened in the second half here.
"We had to sit deep in the first half so Peterborough couldn't get in behind us and use their pace to hurt us - as happened earlier in the season.
"Then we changed formation in the second half to try and put pressure on Peterborough and it got us a goal."