The loss, which leaves the Magpies 12th in the table, ultimately cost Allen the managerial role which he has held since April 2011.
Speaking prior to his dismissal, Allen said: "We've averaged a good return in recent games - been solid and hard to beat. We passed well but didn't have a threat in the final third.
"They looked like scoring each time they went in our box and we got what we deserved. Individually there was no good performances, a lot of players will be disappointed with their performances and it's not good enough for this club that's for sure.
"Our performance was nowhere near what we want, every time they smashed the ball forward they were dangerous. Their goal was a free header from eight yards, it's so disappointing. We've kept clean sheets of late, defending as a team and the first was particularly disappointing. We are all disappointed with that goal."
Hartlepool had coasted to a 3-0 win over County, climbing up to ninth in the table in the process.
After a first loss in six games at Preston in midweek, Pools deservedly went ahead after 38 minutes. Evan Horwood crossed from the left and midfielder Antony Sweeney was free to head home from 10 yards out.
After 55 minutes Sweeney grabbed a second. A well-weighted Andy Monkhouse pass played in the advancing Neil Austin and, from his low cross, Sweeney swept in his sixth of the season and his fourth in five games.
Sweeney then set up Monkhouse for the third, playing a low reverse pass for the attacker to cut inside and curl in a low finish.
The Owls saw city rivals Sheffield United move further ahead of them as the Blades won at home while leaders Charlton were held at Tranmere and are now only six points clear of United.
Runaway leaders Charlton came from behind to claim a 1-1 draw at Prenton Park as they stretched their unbeaten run to seven matches and left Tranmere winless in nine.
Tranmere went ahead after 33 minutes when a speculative angled overhead shot by Martin Devaney was touched on by Ryan Brunt and beyond Ben Hamer into the far corner.
The Charlton equaliser came with an hour gone as Michael Morrison headed home Dale Stephens's corner via the crossbar.
Tranmere almost regained the lead five minutes later but an Adam McGurk free-kick was turned onto the post by Hamer.
A Preston side boasting seven Graham Westley signings in the starting line-up lost 2-1 at Sheffield United despite taking a first-half lead.
Graham Cummins bagged his fist goal for North End to give the visitors the lead, but Ched Evans scored twice after missing a first-half penalty.
Evans was fouled by Aaron Brown inside the area shortly after the half hour, only for Lilywhites goalkeeper Thorsten Stuckmann to thwart his weak effort.
John Bostock fouled Nicky Ajose with 12 minutes remaining and Morgan dispatched the spot-kick in front of 2,800 Owls fans who had seen their team squander several first-half chances.
Daniel Powell scored twice as rampant MK Dons netted four second-half goals to crush hapless Oldham 5-0.
Dean Bowditch's penalty had given Karl Robinson's men a slender half-time lead, but Powell's double and further strikes from Mathias Doumbe and Stephen Gleeson emphatically sealed their first win in six games.
Rochdale lifted themselves off the bottom of the table with a last-gasp 1-0 win over play-off chasing Bournemouth thanks to a Gary Jones penalty in stoppage time.
Yeovil came from behind to see off Colchester 3-2 and provide a huge boost to their survival hopes.
The U's showed their pedigree in the first half and duly went ahead after 19 minutes when Martin Rowlands fed Steven Gillespie on the right and the striker cut in to fire past Sam Walker for his fifth goal in five games.
And that was how it remained until Yeovil's revival began after 55 minutes. A great throughball by on-loan midfielder Lawson D'Ath sent fellow loanee Dean Parrett clear and he slipped the ball past goalkeeper Ben Williams.
It was D'Ath who put Yeovil ahead after 70 minutes, following up after Jon Obika's shot was beaten out, and two minutes later Andy Williams made it 3-1 with a close-range finish from Gavin Williams' left-wing corner.
In a dramatic finale Yeovil brought on substitute Kieran Agard after 88 minutes and he was quickly sent off in stoppage time for a two-footed tackle on Rowlands.
And there was still time for Rowlands to smash the resulting free-kick into the top corner from 30 yards.
Three goals in a scintillating first half helped Exeter to a 3-2 victory over Bury at St James Park.
The hosts made a flying start and found themselves 2-0 up inside the opening nine minutes. The first goal came when Billy Jones' corner kick found its way to Troy Archibald-Henville and he headed home his second goal of the season.
Daniel Nardiello quickly made it 2-0 after Jake Taylor was fouled by Efe Sodje inside the box and the former Manchester United trainee coolly dispatched the penalty into the bottom corner.
Liam Sercombe saw his shot hit the underside of the crossbar for Exeter before Bury pulled a goal back when David Amoo finished from close range after a goalmouth scramble.
Richard Logan made it 3-1 just before half-time when he nodded in at the back post after a brilliant run and cross by Taylor.
After the excitement of the first half, the second was much quieter with chances few and far between. Bury had the better of it and substitute Ashley Eastham capitalised on some shoddy defending by Exeter at a corner, but his goal came too late in the day for the visitors.
Second-half goals from Josh Walker, Andy Barcham and Jon Parkin kept Scunthorpe out of the relegation zone with a 3-1 victory at Leyton Orient.
Jonathan Tehoue gave the Os the lead when he headed home Dean Cox's left-wing cross after 34 minutes. The Iron came to life after the break and levelled after 61 minutes when Walker slammed home a first-time volley from eight yards out after Mark Duffy had opened up the home defence.
Substitute Barcham had been on the pitch for just four minutes when he stabbed home a cross from Garry Thompson in the 85th minute. The visitors ensured the win when Parkin drove home from close range after Orient goalkeeper Lee Butcher had dropped the ball after falling awkwardly.
To compound the misery for Russell Slade's side, Butcher left the field on a stretcher immediately afterwards and central defender Scott Cuthbert took over in goal.
Two second half goals condemned Wycombe to a 2-0 defeat against fellow strugglers Walsall.
Kevan Hurst put the Saddlers ahead with a blistering 63rd minute drive - his third goal of the season - and George Bowerman added the second from a pass by fellow substitute Jon Macken.