Danny Cowley ruled Portsmouth out of the automatic promotion race after losing 2-1 at home to Burton in League One.
Mike Fondop and Josh Powell scored either side of half-time as Burton ended Cowley’s 100 per cent record as Pompey boss.
Portsmouth remain in the top six, but are 12 points off second-placed Peterborough with seven games to play.
Cowley said: “The overriding emotion is frustration. We conceded a really soft first goal and when you do that against a team like Burton you make it really difficult for yourselves.
“We did not have the execution in the final third and rushed plenty of chances. We forced it a little bit and lacked movement.
“We only had three attacking senior players fit and that did not help us.
“Our quality in the final third was a bit short in the second half and there is definitely work for us to do in that area.
“We should not be getting beat at Fratton Park because we are Portsmouth Football Club. I do not expect us to lose these games even though Burton is a good away team.
“I did not think the top two was available to us before today. We have won four games so we have to suck up the disappointment of today.”
A first half devoid of any real chances burst into life in the last minute of normal time when Tom Hamer’s long throw caused havoc in the Pompey defence. Fondop’s initial header was miraculously saved by Craig MacGillivray but he hooked the rebound into the Pompey net.
Powell doubled the visitors’ lead two minutes after the break, turning in Sean Clare’s cross.
Charlie Daniels’s header two minutes from time proved no more than a consolation goal for Pompey as Cowley slipped to his first defeat since replacing Kenny Jackett as boss.
Burton manager Jimmy Floyd Hasselbaink was satisfied after his team moved 10 points clear of the relegation zone.
“I am really pleased with the result and that we scored the goals at the right time,” he said.
“After that we managed to defend extremely well throughout the game. My dressing room was full of tired and battered players who have put everything into the game and managed to get us the three points I think we deserved.
“I thought we were the better team in the first half but Pompey never stop trying and put us under severe pressure.
“I felt a little disappointed with their goal but I’ll have to have a look at it to see where we can improve.”