Portsmouth caretaker-boss Guy Whittingham said his side's first-half display was not acceptable after an early defensive meltdown saw them lose 3-2 at home to Colchester.
Gavin Massey put Colchester ahead after just two minutes, but Jed Wallace's volley levelled the scores three minutes later.
Sam Sodje's clumsy tackle on Freddie Sears handed Colchester a penalty, which Sears coolly dispatched after 15 minutes before Massey's deflected strike made it 3-1 to Colchester five minutes later.
James Keene pulled one back for Pompey after 73 minutes, but their second-half pressure wasn't enough to prevent a seventh straight defeat.
While the Blues were by far the better side after the break, Whittingham was fuming with his side's commitment in the first half.
He said: "Of course, I am pleased with the second half. But if we're not careful, we're in danger of just being pleased we put in a good performance in the second half.
"Well, that's not good enough. You've got to give a good performance in the first and second half to win games."
Colchester manager Joe Dunne hailed the U's resilience as they picked up a second consecutive league victory.
Dunne said: "We've spoken about the fact we haven't scored enough goals, but we've been working exceptionally hard in training defensively and offensively and we're glad that has paid off.
"I thought we were resolute. A few weeks ago, we probably would have crumbled."