Derby head coach Steve McClaren sounded a warning to his players despite a thrilling 4-2 win over Watford at the iPro Stadium that ended the visitors faint play-off hopes.
McClaren saw his team clinch third place with a fifth straight victory but warned that they have to improve to win promotion through the play-offs.
Derby had been caught cold when Troy Deeney fired in his 23rd of the season to give Watford a fifth minute lead but their response was exceptional and they swarmed all over the Hornets for the rest of the first half.
Jeff Hendrick equalised in the 28th minute and former Watford defender Craig Forsyth put them ahead on the hour with a rising drive but the visitors hit back after Marco Cassetti was sent off for a second yellow card by levelling through Mathias Ranegie's header.
But a 25 yard drive from Hendrick in the 82nd minute followed by Chris Martin's 23rd of the sealed it for Derby although McClaren was still left with concerns.
"For the second game in a row we've been sloppy," he said. "Poor defending, giving the ball away and it nearly cost us again. If we do that in the play-offs, there's no chance we'll go through.
"Credit to the players, they keep getting themselves out of a hole and getting the results but in terms of the way forward we certainly need to tighten up in a few areas.
"We scored four but we're not ruthless enough in that and it's ruthlessness at both ends that we need. If we make those kind of mistakes in the play-offs it will make our job very difficult.
"What we have tried to do is provide consistency, not just in results but in performance and that's what we need to get back to, making it difficult for opponents and not thinking we can just go out and outscore them."
For Watford manager Giuseppe Sannino, the performance was a huge disappointment after the way they played at QPR on Easter Monday.
When asked why they were so poor in the first half, he said: "You anticipated me but I would disagree with you in that it was not only the first half, I think Watford are still in London!
"On Monday I said it was the best performance of my regime but for today, I have to say sorry to everyone, all the supporters that came here today. But sometimes football is like that, you have a good performance and then straight after you have this kind of performance.
"What is very disappointing for me is that we didn't show the right anger today to win this game. I am looking for a strong finish to have an assessment of which players can help us next season and to show a good commitment to the club and the supporters."
Derby's victory equalled the club's record points haul for a season of 84, last recorded eight years ago when they won promotion through the play-offs under Billy Davies.