Chelsea missed a host of chances as they were beaten 1-0 at second-tier Middlesbrough in the League Cup semi-final first leg at the Riverside Stadium on Tuesday.
Mauricio Pochettino's side were beaten by a first-half goal from Hayden Hackney but only after Cole Palmer spurned a host of opportunities in the opening 45 minutes.
Leading the line due a host of injuries, the summer signing from treble winners Manchester City could have had a first-half hat-trick but clearly left his shooting boots down in London.
Palmer pulled one shot wide of the target after being gifted possession by home captain Jonathan Howson and fired his next chance over the bar from close range after a spill by goalkeeper Tom Glover.
The 21-year-old was then denied by Glover after cutting in from the left to cap a frustrating half for the Premier League side.
The match had started in disastrous fashion for Middlesbrough – who are currently 12th in the Championship table – with both striker Emmanuel Latte Lath and left wing-back Alex Bangura being forced off injured in the opening 20 minutes.
But that did not stop the north-east club taking the lead in the 37th minute. A fine ball over the defence by Dan Barlaser put Isaiah Jones down the right channel and the winger then provided a perfect low pass for Hackney to score.
Despite all of Chelsea's possession and efforts on goal, it turned out to be the winner giving Middlesbrough a narrow advantage going into the second leg on January 23.
“The way they stuck together was very special and makes me proud to see that. It was great to see and a great feeling, said Boro manager Michael Carrick.
“I thought we managed the spaces well, they had some opportunities and we had to ride our luck a bit at times. We had to show a bit of everything and I'm buzzing.
"Football is about dreaming and things happen like tonight which probably shouldn't happen. We go there with our eyes wide open and know what to expect, but it won't stop us trying.”
As for his opposite number Pochettino, the Argentine expressed his frustration at the missed chances in front of goal.
“If you assess the performance, then overall we were the better side, we created more chances and had the clear chances. But, we didn't score,” said the former Tottenham Hotspur and Paris Saint-Germain coach.
“That has happened this season and there has been a lot of games we have not won because we were not clinical enough.
“We have a lack of goals, but not creating chances. We are creating many chances but not scoring them and if you don't score then it is difficult to win.”
Liverpool face Fulham in the other semi-final first-leg on Wednesday, with the final taking place at Wembley on February 25.
