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 but are currently 12th in the Championship, had chances on the counter-attack to increase their lead but will still head to London believing they can reach Wembley.

Chelsea's players were booed by some of their own fans at the final whistle with Thiago Silva acting as peacemaker but they will be confident of making amends in the second leg on Jan. 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.

"I know it's a two-legged affair and it's still all to play for but with all we've had to go through with injuries and setbacks to beat a team with Chelsea's quality is unbelievable," Carrick said. "It was an exceptional effort."

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.

"That has happened this season and there has been a lot of games we have not won because we are not clinical enough," Pochettino said.