Chelsea suffered a surprise 1-0 loss at second-tier Middlesbrough in the first leg of their League Cup semi-final on Tuesday with Hayden Hackney's goal giving Mauricio Pochettino's wasteful side plenty to do in the return.

The 21-year-old Hackney's silky finish from an Isaiah Jones pass stunned the visitors in the 37th minute at the Riverside Stadium and the hosts defended superbly to take a slender advantage to Stamford Bridge.

Chelsea only had themselves to blame though as they dominated possession but squandered a host of chances — the biggest culprit being Cole Palmer who failed to hit the target twice in the opening half with the goal gaping.

Boro, who won the trophy in 2004, had chances on the counter-attack to increase their lead but will head to London believing they can reach Wembley.

Chelsea's players were booed by some of their own fans at the final whistle but will have the chance to make amends in the second leg on January 23.

Liverpool host Fulham in the first leg of the other semi-final on Wednesday.

Chelsea's stuttering first season under Pochettino has been a case of one step forward and two back and Tuesday was a prime example of the problems they face as they were unable to beat Michael Carrick's injury-ravaged Boro.

They had 18 goal attempts, the majority in the first half, but once again they lacked quality in front of goal and were often exposed in defence.

"We made some mistakes in the first half and gave them chances to score," Pochettino told Sky Sports after his side's ninth defeat of the season in all competitions.

"After that, they were aggressive and played with a deep block and it was hard for us to break them down. But we have another 90 minutes and we need to be positive."

For former Manchester United and England midfielder Carrick, and a raucous home crowd, it was a special night.

Boro began on the front foot but were forced into early changes with Emmanuel Latte Lath and Alex Bangura both hobbling off within the opening 20 minutes.

Palmer should have put Chelsea in front when he was gifted the ball by Jonny Howson but fired wastefully wide.

Minutes later Boro took the lead when the lively Jones did superbly to latch on to a long pass and bamboozle Chelsea left-back Levi Colwill before squaring for Hackney to guide the ball past Djordje Petrovic from close range.

Palmer wasted an even better chance in first-half stoppage time as he sliced over from in front of goal after Boro keeper Tom Glover failed to gather a shot by Enzo Fernandez.

And Palmer was denied again before the halftime whistle, this time taking too long to shoot and then firing too close to Glover who had a superb game.

Chelsea monopolised the ball in the second half but lacked the guile to break down Boro's red wall.

Boro are 12th in the Championship and lost to Aston Villa 1-0 on Saturday in the FA Cup third round.

“To beat a team of the quality of Chelsea, in any circumstances for us, is unbelievable,” said Middlesbrough manager Carrick. ”The lads were just exceptional. It was an incredible night."

Pochettino's side had scored in their past six games but must improve in the second leg if the Argentine boss is going to retain a chance of winning his first trophy in England at the end of February.

Among English Premier League sides, only Bournemouth and Nottingham Forest (32 each) have lost more games than Chelsea (31) in all competitions since the start of last season, while no team have lost more away from home than the Blues (21) during that period.

Thiago Silva and a handful of other players approached some angry Chelsea fans at full time, but Pochettino insisted "they were fantastic with us" and that his fans were "reacting to Middlesbrough fans", with his players "trying to calm our fans".

Chelsea's recent investment can be highlighted by the fact that only two of the squad who played in an FA Cup tie against Boro in January 2022 are at the club this season, and while summer signing Palmer has been a shining light so far, this was a difficult night for the 21-year-old.