Phil Brown was "alarmed" at mistakes which gifted Middlesbrough a 3-1 win and poured more uncertainty over Hull City's survival.
Brown was disappointed with the first mistake in the third minute as Kamil Zayatte failed to clear a long ball allowing Afonso Alves time to shoot. His effort was parried by Matt Duke but straight into the path of Tuncay who slotted home.
But minutes later on-loan Hull striker Manucho rose highest to head home a Nick Barmby cross and bring the game back on level terms.
However that was short-lived when Boro defender Matthew Bates stole a yard on his marker to clip home a Tony McMahon corner just before the half-hour mark.
As Hull piled on more pressure in the second half, former Tigers hitman Marlon King cemented the away side's fate when he latched onto a George Boateng mistake to fire past Matt Duke.
"The reality is the game was not about Middlesbrough's great creativity it was about our mistakes and that was an alarming fact," Brown told Sky Sports.
"When it comes into a situation where you've got six games to go, you've got a lot of pressure on players individually.
"The more opportunity that we can get experienced players out there the better for us I think.
"One or two made mistakes for the first goal, the second goal for me was a mistake from the set-piece and the third goal obviously was gifted to Marlon King on a plate.
"That is the alarming sign."
Hull are now in 15th spot after the setback, however are on the same points as Blackburn who lost 4-0 to Liverpool earlier on Saturday.
But the Tigers manager is welcoming the much-needed returns for Boateng - who came on as a substitute against his former club - and expects Kevin Kilbane and Daniel Cousin to be back to full fitness soon.
"We've got enough experience coming back to full fitness," he said.
"Daniel Cousin will be on the training ground next week to hopefully get us through this tight situation we're in.
"We've got to get something from the game next week then we all hit difficult teams, you're playing against the Manchester Uniteds and the Arsenals.
"We've got to get enough points on board to try and arrest the situation that we're in at the moment in time and hopefully that will start at the Stadium of Light next week."