Dagenham & Redbridge have made an immediate return to League Two after a heavy defeat by play-off bound Peterborough sealed their relegation.
Nathaniel Mendez-Laing put Posh ahead when he slotted past the stranded Tony Roberts, before Darren Currie twice hit the post for the Daggers.
Grant McCann drove in to double the lead and George Boyd fired in a third.
Craig Mackail-Smith and David Ball both scored late on to round off a miserable afternoon for the visitors.
The Daggers needed at least a point to have had any hope of avoiding relegation to League Two.
Just a draw would have seen them avoid the drop and Walsall, who lost 3-1 at Southampton, instead being relegated on goal difference.
Dagenham had plenty of chances to pull level in the first half when John Akinde was twice denied by Posh goalkeeper Joe Lewis and Romain Vincelot headed over.
Peterborough, who will face MK Dons in the play-offs, bossed the majority of the second half, with Tommy Rowe and Mackail-Smith also going close.
Vincelot and Jon Nurse both headed wide for Dagenham, who were well beaten in the end.
They now drop back into League Two, just a year after gaining promotion via the play-offs to the third tier for the first time in their history.
Peterborough United boss Darren Ferguson told BBC Radio Cambridgeshire:
"This win sets us up perfectly for the play-offs and should give us a lot of confidence.
"It's never really mattered who we would play because I feel that if we can play to the best of our ability then we will win.
"That's not me being arrogant, it's what any manager would say. I'm really looking forward to the next couple of weeks."
Dagenham & Redbridge boss John Still told BBC London 94.9:
"We didn't go down today, it's been over 40-odd games, but week after week we have got the maximum out of what we have.
"For our resources we have amazing quality, every year we sell players as that goes to show.
"I think we do produce quality and now we have to find the next lot and I'm proud of what we do.
"I haven't got too much to do, I know exactly what I'm doing, and relaxed about the close season."