Peterborough 6 (Assombalonga 4, Tomlin 19, 54 pen, 79 pen, Swanson 28, Payne 90)
The Royals crashed out of the Capital One Cup with a whimper as a rampant Peterborough side coasted to a comprehensive 6-0 Second Round win at London Road.
Darren Ferguson's men were three goals up before the half hour mark as Britt Assombalonga arrowed home a third minute opener, Lee Tomlin hammered a spectacular second under the crossbar from distance and Danny Swanson picked out the top left corner with a curling 20-yard finish.
Assombalonga won a penalty early after the interval and Tomlin hammered home a fourth from the spot, before completing his hat-trick with a second penalty after Barnett had been pulled back inside the area.
In injury time, Le Fondre saw an effort cleared off the line but moments later Jack Payne drilled home a sixth from distance after substitute Mendez-Laing had struck the crossbar.
Peterborough, who had scored five in the league at the weekend, went one better against the Royals and, in truth, were well worthy of their place in the Third Round and of the six-goal scoreline. A night to fast forget for Reading.
Peterborough: Olejnik, Little, Alcock, Bostwick, Knight-Percival, Payne, Swanson, Rowe (c) (Mendez-Laing 84), Tomlin (Gordon 84), Assabalonga (Anderson 84), Barnett.
Subs: Day, Ntlhe, Brisley, Kearns.
Reading: Federici, Cummings, Gunter, Gorkss (c), Mariappa, Akpan, Williams, Robson-Kanu, Obita, Pogrebnyak, Le Fondre.
Subs: Taylor, Pearce, Morrison, Karacan, Guthrie, Blackman, Drenthe.
Yellow: Akpan, Gorkss, Williams, Le Fondre.
Referee: Mr K Hill
The game burst into life in only the third minute when Peterborough took the lead. Britt Assombalonga cut inside from the left and into the box, gained a yard on Adrian Mariappa and rifled an superb low strike into the bottom left corner for 1-0.
Assombalonga forced Federici into two very good saves moments later, the first a right-footed volley that he directed straight at the Aussie's body as he fell to the ground, and the second a 25-yard drive that Federici leapt to his right to push wide.
Ten minutes in and the Royals had found a foothold and were beginning to pile pressure on the Posh defence. Pavel Pogrebnyak slid in strike partner Le Fondre and Bobby Olejnik had to pull off a smart save low to his left to deny the visitors an equaliser.
But before Nigel Adkins' men could respond, Peterborough scored a stunning second. Lee Tomlin was found on the corner of the box and the striker simply lashed the bouncing ball high over the helpless Federici and whistling under the crossbar for 2-0.
And another quite superb finish made it 3-0 before the half hour mark. This time it was Danny Swanson who scurried forward, checked back onto his right boot and bent a lovely shot around his marker and inch perfect into the top left corner.
Federici had to hurl himself to the right to prevent Tomlin curling a free kick home moments later as the home side, bursting with confidence after a 5-0 win at Tranmere at the weekend, ran riot.
At the other end Obita crossed for Gorkss and Mariappa swung one in for Pogrebnyak, both from the right flank, but Olejnik gathered each headed attempt on target.
Cummings dinked a ball in from the left and Alcock had to head over his crossbar as half-time approached. Obita swung in a tasty corner and Hal Robson-Kanu glanced it goalwards at the near post, only to see Olejnik pull off an incredible save - the Peterborough stopper instinctively clawing it off his goalline and over his crossbar.
In the opening stages of the second half, Le Fondre looked to race onto a long ball from Gunter and through on goal, but the offside flag stopped him in his tracks before he could get a shot away.
And Peterborough added a fourth to put the result beyond any doubt whatsoever. Assombalonga ran at Gorkss and tripped over the Latvian's lunge, referee Keith Hill pointed to the penalty spot and Tomlin buried it.
Robson-Kanu crossed for Le Fondre to head high into the air but it was easy for Olejnik to collect as the Peterborough fans began to celebrate their side's all too comfortable passage into the Third Round.
Federici produced a fingertip save to deny Swanson a second as the hosts broke at pace yet again, while Akpan came close with a drive that skidded through a crowded box and ricocheted away from danger.
Cummings then came close from exactly the same position, forcing Olejnik into a good save, and Mariappa rippled the side netting with a far post header.
But it was the home side who were looking the more likely to add to the scoresheet further, Federici coming to the rescue by pushing a Barnett effort over the crossbar from a tight angle.
Barnett did help the home side pile on more misery, winning a second penalty after he was pulled back by Shaun Cummings inside the box and Tomlin sent Federici the wrong way to complete his hat-trick.
Le Fondre saw a shot cleared off the line in injury time, but Mendez-Laing struck the crossbar moments later and Jack Payne collected the rebound and drilled home a sixth from distance to end the scoring in injury time.
A dismal performance and a Capital One Cup hammering for Reading. A night to forget very quickly.