A second half strike from Tom Cursons was enough to secure victory for Boston United as Posh suffered their first pre-season friendly defeat.
Peterborough United created a host of opportunities in front of goal and were dominant in terms of possession, but were ultimately beaten 1-0 by Enterprise National League side Boston United at the Jakemans Community Stadium.
Luke Williams' side should have scored inside the opening three minutes as Luke Faxon spilled a low cross from Owura Edwards into the path of summer signing Harrison Jones, but the goalkeeper atoned his mistake with a fine stop.
Carl Johnston was next to try his luck from distance, which was more routine for Faxon while Evan Weir's deflected shot was also claimed by the keeper.
There was a clutch of bookings including James Dornelly around the half hour mark before two minutes from time, Posh came close again as Harry Leonard was a whisker away from converting Weir's low centre.
Chris Conn-Clarke saw a curling effort parried by Faxon before Bolu Shofowoke curled his shot over the top after a mistake at the back from the home side.
Brandon Khela saw a clever lob drift past the post on 50 minutes before Shofowoke saw a shot blocked. Andeng Ndi made a fine stop with his legs to keep out substitute Cursons and on 72 minutes made a double stop, again denying Cursons and the rebound from the trialist.
On 74 minutes, Boston did open the scoring as CURSONS raced clear and coolly found the bottom corner past Andeng Ndi. Posh should have found a leveller late on with Abbey picking out the trialist, but he couldn't squeeze the ball past the keeper.
Harley Mills lashed a shot wide while the hosts also came close in stoppage time as the game ended in a 1-0 win for the Pilgrims. Posh are next in action at York City on Tuesday evening.
Boston: Faxon, Sachdev, Shipley, Ward, Trialist F, McBride, John-Lewis, Trialist D, Grimes, Agyemang, Pozo. Subs used: Teale, Holmes, Cursons, Lankshear, Hammond, Rooney, Mauro, Trialist E, Grist, Raikhy, Chadwick.
Posh: Andeng Ndi, Dornelly (sub Freeman 46min), Andrews, Okagbue (sub Mendonca 46min) , Weir (sub Mills 60min), Johnston (sub Khela 46min), Jones (sub Fox 60min), Edwards (sub Trialist A 60min), Conn-Clarke (sub Sykut 60min), Shofowoke (sub Abbey 60min), Leonard (sub Kamara 46min).
Attendance: 1,435 (476 Posh fans)
Half-time: Boston United 0-0 Peterborough United
Full-time: Boston United 1-0 Peterborough United
Referee: Declan Bourne