Chelsea boss Mauricio Pochettino bemoaned a familiar lack of cutting edge after his team lost the first leg of their League Cup semi-final 1-0 to Championship side Middlesbrough at the Riverside on Tuesday.

Hayden Hackney scored the only goal on 38 minutes as Pochettino's expensively assembled array of stars again failed to perform away from home.

Chelsea have lost five of their last six away games and 21 times on the road since the beginning of last season -- the most of any Premier League team.

The Blues must turn the tie around when the sides meet again at Stamford Bridge on January 23 to avoid heaping more pressure on Pochettino's position during a disappointing first season in charge for the Argentine.

"If we assess the performance overall we were the better side, had clear chances, but we didn't score and weren't clinical," said Pochettino. "It happened a lot this season."

Boro boss Michael Carrick could have been forgiven for cursing his luck after losing top scorer Emmanuel Latte Lath to injury after just three minutes.

Carrick was also forced to withdraw Alex Bangura inside 20 minutes but the second-tier side were not fazed.

"It's very special," said the former Manchester United midfielder. "I know it's a two-legged affair and there is still all to play for, but for what we've had to go through, the injuries, the setbacks we've had, to beat a team of Chelsea's quality is unbelievable."

Middlesbrough had not scored against Chelsea for over 17 years. The Blues had won the past nine meetings by an aggregate score of 21-0.

However, the home side ended that drought eight minutes before half-time.

The pace of Isaiah Jones down the right caused Chelsea's makeshift left-back Levi Colwill problems all night and his low cross was turned in by Hackney from close range.

ALSO READ |&nbsp;<a href="https://www.wionews.com/cricket/former-south-africa-player-cites-virat-kohlis-example-to-keep-tests-as-priority-over-t20-leagues-678327">Former South Africa player cites Virat Kohli's example to give Tests priority over T20 leagues</a>

<h2>Profligate Palmer</h2>

Chelsea, though, should have at least been level at the break had Cole Palmer maintained his fine scoring form in front of goal.

The former Manchester City academy graduate has been one of Chelsea's few big money signings to hit the ground running under Pochettino.

However, Palmer twice failed to hit the target with glorious first-half chances.

Firstly, he pulled his shot wide from the edge of the area after pouncing on an errant pass from Jonny Howson, and then he fired over the rebound after Tom Glover fumbled Enzo Fernandez's effort.

Palmer then fired too close to Glover with another big chance just before the break.

The flow of the second half was a different story as Chelsea pegged the home side back in search of an equaliser.

But there was a familiarity to the visitors' inability to find a way through.

Despite the club spending over £1 billion ($1.3 billion) on players in the last three transfer windows, Pochettino suggested last month he would need to look to strengthen once more in order to address the lack of a goal threat.

Noni Madueke looked the most likely spark to Chelsea's attack, but he was sacrificed as Pochettino threw on Mykhailo Mudryk and Armando Broja.

Raheem Sterling should have been more alive to meet one dangerous low cross from Broja, but that was all Chelsea's vast amount of possession in the final 20 minutes amounted to.

Middlesbrough conceded late to lose 1-0 to Aston Villa in the FA Cup third round on Saturday.

But this time the team that sit 12th in the Championship held out to keep their dreams of a Wembley final against either Liverpool or Fulham very much alive heading into the second leg.

Chelsea boss Mauricio Pochettino bemoaned a familiar lack of cutting edge after his team lost the first leg of their League Cup semi-final 1-0 to Championship side Middlesbrough at the Riverside on Tuesday.

Chelsea boss Mauricio Pochettino bemoaned a familiar lack of cutting edge after his team lost the first leg of their League Cup semi-final 1-0 to Championship side Middlesbrough at the Riverside on Tuesday. Hayden Hackney scored the only goal on 38 minutes as Pochettino's expensively assembled array of stars again failed to perform away from home. Chelsea have lost five of their last six away games and 21 times on the road since the beginning of last season -- the most of any Premier League team. The Blues must turn the tie around when the sides meet again at Stamford Bridge on January 23 to avoid heaping more pressure on Pochettino's position during a disappointing first season in charge for the Argentine. "If we assess the performance overall we were the better side, had clear chances, but we didn't score and weren't clinical," said Pochettino. "It happened a lot this season." Boro boss Michael Carrick could have been forgiven for cursing his luck after losing top scorer Emmanuel Latte Lath to injury after just three minutes. Carrick was also forced to withdraw Alex Bangura inside 20 minutes but the second-tier side were not fazed. "It's very special," said the former Manchester United midfielder. "I know it's a two-legged affair and there is still all to play for, but for what we've had to go through, the injuries, the setbacks we've had, to beat a team of Chelsea's quality is unbelievable." Middlesbrough had not scored against Chelsea for over 17 years. The Blues had won the past nine meetings by an aggregate score of 21-0. However, the home side ended that drought eight minutes before half-time. The pace of Isaiah Jones down the right caused Chelsea's makeshift left-back Levi Colwill problems all night and his low cross was turned in by Hackney from close range. ALSO READ | Former South Africa player cites Virat Kohli's example to give Tests priority over T20 leagues Profligate Palmer Chelsea, though, should have at least been level at the break had Cole Palmer maintained his fine scoring form in front of goal. The former Manchester City academy graduate has been one of Chelsea's few big money signings to hit the ground running under Pochettino. However, Palmer twice failed to hit the target with glorious first-half chances. Firstly, he pulled his shot wide from the edge of the area after pouncing on an errant pass from Jonny Howson, and then he fired over the rebound after Tom Glover fumbled Enzo Fernandez's effort. Palmer then fired too close to Glover with another big chance just before the break. The flow of the second half was a different story as Chelsea pegged the home side back in search of an equaliser. But there was a familiarity to the visitors' inability to find a way through. Despite the club spending over £1 billion ($1.3 billion) on players in the last three transfer windows, Pochettino suggested last month he would need to look to strengthen once more in order to address the lack of a goal threat. Noni Madueke looked the most likely spark to Chelsea's attack, but he was sacrificed as Pochettino threw on Mykhailo Mudryk and Armando Broja. Raheem Sterling should have been more alive to meet one dangerous low cross from Broja, but that was all Chelsea's vast amount of possession in the final 20 minutes amounted to. Middlesbrough conceded late to lose 1-0 to Aston Villa in the FA Cup third round on Saturday. But this time the team that sit 12th in the Championship held out to keep their dreams of a Wembley final against either Liverpool or Fulham very much alive heading into the second leg.

League Cup: Middlesbrough stun Chelsea to take semifinal lead in first leg

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League Cup: Middlesbrough stun Chelsea to take semifinal lead in first leg