Middlesbrough's 1-0 injury-time Championship defeat by Bristol City was a result of key players failing to perform, says head coach Aitor Karanka.
The Teessiders saw their lead at the top cut to two points, and the loss ended a run of five consecutive wins.
By contrast the Robins secured a double over Boro, who were under interim coaches John Pemberton and Wade Elliott following Steve Cotterill's sacking.
"I expected more from the important players," Karanka told BBC Tees.
"When those players had to appear they didn't, when those important players don't appear, it's difficult."
Although promotion rivals Hull were convincing winners, beating Charlton 6-0, one saving grace for Karanka's side at the top of the division was Derby's 3-0 home defeat by Birmingham.
The Rams have stuttered since the turn of the year and are without a win in four, with Blues boss Gary Rowett touching on 'nervousness and vulnerability' among the Derby players at a crucial stage of the season.
The pressure to maintain form is something Boro boss Karanka is also concerned about among his squad.
"We are the team, we have to be always thinking about ourselves, so for that reason we are really disappointed," the Spaniard said.
"I said sometimes it's difficult for the players when everyone is expecting the best when we are on a good run, people can sometimes expect an easy game.
"That can bring pressure, sometimes it's easy to play against a big, big team."