Defensive rock Mark Arber became an unlikely goal hero as his cracking double-strike lead Posh to victory over their play-off rivals.
The ever-present defender hadn't scored all season before this crucial contest, but he broke his duck in considerable style to continue Steve Bleasdale's impressive start in the Posh hot-seat.
But it wasn't all plain sailing for Posh as the combination of a swirling wind and awful playing surface made for testing conditions.
In fact they found themselves trailing after 27 minutes when a goalkeeping howler from Lee Harrison was punished by Darlington debutant Andy Cooke.
The veteran former Burnley and Stoke striker marked his first Quakers appearance since a loan move from League One club Bradford by sweeping the ball into an empty net after pressuring Harrison into a punching error.
The lead lasted until two minutes before the break when Arber collected a lay-off from leading scorer Danny Crow before sending a rasping drive past Darlington keeper Sam Russell.
That goal was no more than Posh deserved for producing the most enterprising attacking moments of the opening half.
Both Crow and Northern Ireland international strike partner James Quinn had gone close either side of the Darlington opener.
And both teams spurned good opportunities in the second half before Arber settled the contest with 15 minutes remaining.
Crow and substitute Adam Newton combined to unlock the Darlington defence down the right flank, with the latter delivering a low cross that Arber coolly stroked past Russell from a tough angle.
Harrison redeemed himself after his costly slip with a brave block at the feet of Quakers substitute Simon Johnson and he was required to make another important late interception to guarantee maximum points for Posh by thwarting Kyle Lafferty in stoppage time.