Tranmere boss Ronnie Moore refused to criticise goalkeeper Owain Fon Williams after Derby ran riot in a 5-0 FA Cup victory.
League One leaders Rovers, 15 places below the Rams, initially started well but once Ben Davies capitalised on Fon Williams' mistake in the 42nd minute, there was no way back.
Former Wigan striker Conor Sammon scored a second - his seventh of the season - and John Brayford made it a trio of goals in 21 minutes.
Jeff Hendrick added a fourth before Mason Bennett struck to round off the scoring.
Moore acknowledged his keeper's error of letting Paul Coutts' tame shot squeeze under him and into Davies' path was the crucial moment in the match.
"The turning point for me was the first goal," he said. "I thought we probably edged the first half so to concede was disappointing for us.
"We were flat at half-time but, to be fair, the keeper has been fantastic for us this season.
"He's made some unbelievable saves and he feels deep down he should have saved it but I'm not going to criticise him. He'll come back and hopefully keep a clean sheet next week.
"The basic defending just after half-time was poor and really, we gifted them three goals but I think we can take a lot of positives out of the first half.
"I didn't think 5-0 was a reflection on how the game was. The last time we got beat 5-0 we won three league games on the trot ."