Chelsea's need for January signings clear as Mauricio Pochettino's side crumble under pressure in Carabao Cup

Chelsea were beaten in one of their most important matches of the season, losing the first leg of the Carabao Cup semi-final to Middlesbrough.

Hayden Hackney scored the game's only goal, with the only consolation for Chelsea that they have a second leg to come at Stamford Bridge.

Mauricio Pochettino had told his team to take their Championship opposition seriously and they started well, but ultimately cracked in a fiery atmosphere in the North East.

It was Chelsea's first loss to lower-league opposition in 16 domestic cup matches.

Colwill is not a left-back

Michael Carrick knew Levi Colwill would play at left-back and his game-plan was to exploit that.

Winger Isaiah Jones had the beating of the 20-year-old and gave them the outlet they needed to release the pressure.

Jones set up the Middlesbrough goal by outpacing Colwill before cutting it back to midfielder Hackney.

On the night Ian Maatsen flew to complete his loan move to Dortmund, Chelsea looked like they needed a left-back.

False nine experiment

Cole Palmer started up front for Chelsea as Armando Broja was left on the bench.

He missed a host of chances, including an open goal, a one-on-one and several edge-of-the-box efforts, which he usually thrives on.

Palmer didn't look the best option as a striker when Broja could have been that target man. As Broja entered the field, the Blues had put in 21 crosses but didn't have a target man to hit.

If Pochettino doesn't trust Broja in one of the season's biggest games, with Nicolas Jackson at the African Cup of Nations for another month, maybe they need to dip into the transfer market.

Weak mentality again

Chelsea weren't that poor in the first half but simply missed big chances.

They were punished by a goal against the run of play, but normally when that happens to big teams, they keep playing their football.

Instead, Chelsea crumbled and got worse in the second half, creating few chances and ending up looking like a team that deserved to lose.

Axel Disasi's terrible 35-yard strike summed up the resignation from a group of players that crack at the first sign of hardship.