Goals from Mark Cullen and Brad Potts saw Blackpool win their third game on the bounce.
The Seasiders were superb from start to finish in monsoon type weather at Bloomfield Road.
Pool had just a minute to wait to take the lead, Mark Cullen reacted quickly to finish after his penalty was saved by Ben Alnwick in the Peterborough goal.
As Blackpool soaked up the pressure, just after the half hour mark they doubled their lead.
After Cullen caused havoc Potts broke from midfield to pick up the loose ball, round Alnwick and tap into an empty net.
From then on in it was a lesson in defending for the Seasiders, who restricted their visitors to long-range efforts all afternoon.
It’s a result which sees them create a four-point gap from the drop-zone, McDonald will be rightly delighted.