Birmingham City became odds on favourites at 8/11 with Sky Bet after their recent win over Wrexham.
They are a big club by League One standards and they’ve flexed some serious financial muscle following their relegation from the Championship last season.
But it’s nothing Posh haven’t faced, and beaten, before at this level in the Darragh MacAnthony/Darren Ferguson eras. Here are some of the most memorable wins against the big boys in League One.
1. Posh 2, Leeds 0, 2008.
Second-half goals from George Boyd and Craig Mackail-Smith (pictured) sealed the home win for a team who would be promoted as runners-up behind Leicester City that season. Leeds finished fourth and lost to Millwall in the play-off semi-finals. Photo: PT
2. Posh 2, Leicester City 0, 2009.
Charlie Lee (pictured diving after scoring) and Chris Whelpdale scored as Posh beat the table-toppers in front of a capacity London Road crowd. Huddersfield and Brighton were other future Premier League clubs who didn't win promotion from League One that season. Photo: PT
3. Posh 2, Leicester City 0, 2009.
Chris Whelpdale celebrates his goal against Leicester in March 2009. Photo: PT
4. Posh 5, Sheffield Wednesday 3, 2011.
Posh came from 3-2 down at half-time to topple Wednesday at London Road on a February night with goals from George Boyd (2), CRaig Mackail-Smith (2) and Nat Mendez-Laing (pictured). Photo: Alan Storer