Peterborough manager Darren Ferguson admitted he was "embarrassed" by their 4-0 thrashing by Plymouth and says his side must "toughen up".
League One Argyle eased into the second round for the fourth straight season thanks to a double from Ryan Hardie and goals from fellow strikers Luke Jephcott and Panutche Camara against their Championship opponents.
Posh announced the signing of Shrewsbury midfielder Oliver Norburn a few hours before kick-off, but boss Ferguson had little else to cheer about.
"I was surprised, shocked, embarrassed – it was a real spanking I've got to be honest," Ferguson said.
"We never got started, never got the tempo going.
"I'll take that one on the chin. Maybe we shouldn't have started with that formation, but in saying that the goals we've conceded are too soft and that is a big problem.
"We need to toughen up very, very quickly – we look far too easy to play against."
Hardie fired in low with his left foot on 23 minutes before lashing home from close range 10 minutes later.
Debutant home goalkeeper David Cornell made several good saves but was beaten by Jephcott on 66 minutes when the striker tapped in from a corner, before he turned provider on 84 minutes to allow Camara to fire home at the near post.
Jephcott ended a six-month goal drought, and manager Lowe said: "I'm really pleased with every single player – they were different class.
"Deep down I'm over the moon but we have to keep a level head. I'm delighted that the strikers are off the mark.
"Ryan Hardie was fantastic and should have had a hat-trick. With the strikers scoring goals, as a former striker that's what I want them to do.
"Luke's work rate is phenomenal and if you do that you will get your goals. Long may that continue."
