Exodus Geohaghon's first league goal secured Mark Cooper's maiden victory as Peterborough manager and ensured Watford ended a turbulent week with a 2-1 defeat.
The Hornets only avoided the threat of administration on Friday after majority shareholder Lord Ashcroft agreed to repay a loan of #4.88million to former chairman Jimmy Russo.
And manager Malky Mackay will have been pleased with the way his players acquitted themselves at London Road, especially in the second half, but for Geohaghon's 78th-minute winner.
Lee Frecklington wasted no time giving Posh the lead with a well-taken volley after the Coca-Cola Championship encounter survived a pitch inspection.
Watford, who somehow saw Danny Graham denied a stonewall penalty when he was taken out by the impressive Joe Lewis, levelled in the 48th minute through John Eustace's first goal of the season.
But on-loan centre-back Geohaghon headed home to ensure Posh leapfrogged Plymouth at the foot of the table - with the Championship's bottom side at Christmas being relegated in nine of the last 10 seasons.
It required an immense effort from Peterborough ground staff and those drafted in to even get the encounter under way, with a collection of people still attempting to clear the pitch from snow just five minutes before kick-off.
The decision from referee Karl Evans to give the game the green light was definitely a questionable one with the playing surface resembling more of an ice rink than a football pitch.
But the hosts wasted no time acclimatising to the conditions and took the lead after just nine minutes.
Neat interchange down the left found the impressive George Boyd and he worked his magic before floating an inch-perfect cross the width of the penalty area for an unmarked Frecklington to volley home.
Watford were gifted a great opportunity to level soon after when Tom Cleverley found himself clean through following Paul Coutts' weak header, but a combination of the uncertainty under foot and a poor second touch saw the chance drift away.
An evenly-contested opening quarter was played out before the visitors were denied what appeared to be a blatant penalty shortly before the half-hour mark.
Hornets striker Graham went up for the ball with Posh goalkeeper Lewis before being clattered to the floor, only to receive a yellow card for his subsequent protestations.
Craig Mackail-Smith came within inches to connecting with a certain second for Posh while John Harley dragged wide at the other end prior to the half-time interval.
Remarkably, the pitch was still playable as the second half kicked off but the plummeting temperatures were threatening to turn the playing surface into a sheet of ice.
Yet the players seemed to be unaffected and Hornets goalkeeper Scott Loach dived low to his right to keep out Chris Whelpdale's strike after 16 seconds.
And the save proved crucial as Eustace fired the hosts level within minutes when Posh defender Scott Griffiths failed to fully clear Cleverley's right-wing free-kick.
Watford had a lot more urgency about them after the restart as they peppered the Peterborough goal with shots - Cleverley seeing a well-worked chance smothered by England hopeful Lewis.
The Posh keeper again proved his quality to keep out Heidar Helguson's 68th-minute header but the Iceland international, who did not have an afternoon to remember, should have done better.
And the Hornets were made to pay for their missed chances when Geohaghon headed home after the away side failed to clear Frecklington's corner.
Yet there was still time for Lewis to produce a superb stop to keep out Helguson's header.
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