A controversial penalty decision and some clinical Peterborough finishing combined to leave Carlisle United with nothing to show for their Bank Holiday trip to London Road.
United enjoyed some good early pressure but they were almost undone when Bostwick pounced on a misplaced pass from Symington in midfield. He quickly fed Alcock and a long ball forward found Isgrove on the move. His cross was controlled by Washington but the big striker lost his balance and poked a tame shot wide.
Isgrove was the danger man again moments later when he beat Meppen-Walter to an awkwardly bouncing ball. He spun away and shot from the angle but Pickford dropped low to make a block at his near post.
Peterborough looked bright and Washington took a difficult ball on his toe as it looped over the back line. McQuoid took over but his cross skimmed off Washington's head before heading away to safety.
The home side kept the pressure up and a slip from Symington allowed McQuoid to make the bye line and pump a fizzing cross into the box. Washington timed his run perfectly to volley first time from 14 yards under the dive of the stranded Jordan Pickford.
Carlisle crept into it with some solid work from Berrett and Nacho Novo found himself with a clear run at goal when Dawson pounced on a mistake in midfield. The nippy striker edged forward and brought a full length save from Olejnik as he tried to thunder his shot into the back of the net.
Meppen-Walter had two headed half chances as Berrett popped testing deliveries into the box but Peterborough should have extended their lead when Isgrove once more wound his way through the back line. Assombalonga was in acres of space but the cut back had too much on it and Carlisle were able to clear.
The visitors survived a half-hearted penalty appeal when Isgrove went to ground under pressure from Brown but they stayed forward in numbers and it eventually came to McQuoid on the edge of the box. Potts did well to step across and block the goal-bound shot.
Peterborough looked comfortable but Dawson tried his luck from distance as the visitors tried to ease the pressure. Olejnik watched as it whisked past his upright. Another dangerous Berrett free kick followed but Brown couldn't capitalise as Novo stretched to keep it alive at the far post.
Reece Brown was twice the saviour as half time approached as an important tackle on Isgrove was followed by a clearance off the line as Meppen-Walter lost the flight of a dipping McQuoid corner and almost turned the ball into his own net.
The second half took a while to get going but a hopeful ball over the top from McCann almost opened the door when Assombalonga flicked it on. Washington was through but he lost his footing and screwed a poor shot into the stands.
Controversy ruled on 54 minutes when Assombalonga twisted and turned in the Carlisle area. His cross appeared to hit Brown in the midriff but the referee immediately blew for a penalty despite having had no reaction at all from his assistant, who had a clear view of the incident. Assombalonga ignored the remonstrations and calmly swept the spot kick into the back of the net.
Carlisle quickly worked their way back into the game with a contender for goal of the season from Lee Miller. His touch and control on the edge of the area set him up for a peach of volley which left Olejnik with no chance as it flew into the bottom corner of the net.
The dangerous Assombalonga crunched another difficult first timer at Pickford and Nugent fluffed his lines as the ball got stuck at his feet from a deep corner when he had the width of the target to aim at.
The home side restored their two goal advantage when Assombalonga charged through to go one on one with Pickford. A clip from the keeper brought the second spot kick of the day and the big striker did the rest with another crisp strike.
Brad Potts whipped a curling 30-yarder over the bar as Carlisle kept going but Nthle did the same at the other end as the home side worked hard to see the game out. And Pickford had to stay strong when Ajose broke through to make another vital block as the home side looked to add to their tally.
Assombalonga was denied a hat-trick late in the day by brave defending but a deflected 90th minute shot from Bostwick added to the woes as the Posh made it four for the day with Pickford unable to do anything about it.
Peterborough - Washington (14), Assombalonga (55 pen, 73 pen), Bostwick (90)
United - Miller (63)
Peterborough - Nugent (53)
Peterborough United - Olejnik, Alcock, Ntlhe, Nugent, Baldwin, McCann, Bostwick, Isgrove (Mendez-Laing 78), McQuoid (Rowe 71), Washington (Ajose 80), Assombalonga. Subs - Day, Newell, Payne, Little.
Carlisle United - Pickford, Symington, Meppen-Walter, Thirlwell (Amoo 46), Brown, Robson, Potts, Dawson (Redmond 60), Berrett, Novo (Byrne 75), Miller. Subs - Fleming, Chantler, Guy, Chimbonda.
Referee - Mr David Phillips
Attendance - 5,921 (281 away fans)