Two goalkeeping howlers by Jamie Ashdown cost Crawley dear as they let slip an early lead to lose 4-1 at home to Peterborough.
Town led through a second minute goal by Izale McLeod before the Posh replied with two goals in each half.
Conor Washington scored twice and there was one each for Michael Smith and Marcus Maddison.
John Gregory made four changes to the side which beat Luton Town on Tuesday in the Johnstone’s Paint Trophy.
He was missing both Gwion Edwards and Joe Walsh who are on international duty with the Wales senior squad for the European qualifiers.
Izale McLeod, Jimmy Smith, Lanre Oyebanjo and Jamie Ashdown returned in place of Matt Harrold, Bobson Bawling, Brian Jensen and Gwion Edwards.
Reds took an early lead with the first attack of the game in only the second minute when a move involving Lewis Young and Gavin Tomlin was put away with a good finish by McLeod.
Peterborough immediately reponded with a series of attacks which included four successive corners and which put the home defence under pressure.
The spell paid off as Peterborough equalised on 12 minutes following a mistake by keeper Ashdown who dropped a cross by Joe Newell which led to Michael Smith firing on the rebound into the top of the net.
Marcus Maddison had a shot from 25 yards saved by Ashdown.
McLeod received treatment on an injury and although he tried to continue had to be taken off and was replaced upfront by Matt Harrold, who was soon in the thick of the action.
Harrold headed a corner over the bar and then had the ball cleared from his feet by keeper Ben Alnwick as Crawley looked for a second goal.
Maddison lifted a chance well over for the visitors after a one-two with Conor Washington while for Reds, Marvin Elliott went wide with an overhead kick.
Bradley nodded down a ball for Dean Leacock to have a go on the volley but his effort was tiopped over the bar by Alnwick.
Peterborough took the lead in the 32nd minute from a corner kick which was headed in off tream-mate Washington by Christian Burgess, who was wearing a protective mask for a broken nose suffered two weeks ago.
Crawley had a good breakaway attack after the break in which Young shot well over the bar.
But Peterborough finished the game off by scoring twice in two minutes.
Keeper Ashdown made his second blunder of the afternoon when he passed the ball directly to striker Maddison who made easy work of tapping-in the visitors’ third goal.
To rub salt into Crawley’s wounds, Washington added a fourth goal in the 57th minute when Joe Newell played the ball into the box and he hit a superb strike.
Ashdown pulled off a fine diving save to deny Washington a fifth after 66 minutes.
There was no prospect of a late fightback from being so far down with Peterborough keeping most of the possession.
REDS: Ashdown, Oyebanjo, Leacock, Bradley, Smith, McLeod (Harrold 23), Young, Keane, Tomlin (Banya 83), Sadler, Elliott.
Unused sub: Jensen, Henderson, Bawling
POSH: Alnwick, M.Smith, Baldwin, Bostwick, Taylor (McEvoy 81), Payne, Washington, Anderson (McCann 81), Newell, Burgess, Maddison (Oztumer 90.
Unused subs: James, Oztumer, McCann, Ferdinand, McEvoy, Santos, Grant
REFEREE: Michael Bull
ATTENDANCE: 2,832 (494 away)