Middlesbrough will take a 1-0 lead to Chelsea on January 23 after beating the Premier League side in the first leg of their Carabao Cup semi-final on Tuesday.
Hayden Hackney scored the only goal at the Riverside Stadium as the team 12th in the Championship recorded a narrow win over the outfit 10th in the EPL.
Hackney's goal arrived in the 37th minute from one of Boro's six shots.
At the other end, Chelsea recorded 18 shots - five of which forced saves out of keeper Thomas Glover.
But it was not just Glover's brilliance that resulted in Boro's clean sheet. Chelsea's finishing was pretty awful too.
Cole Palmer could have scored a hat-trick but the former Manchester City youngster had a torrid time in front of goal.
Palmer produced what was widely described on social media as the "Miss of the Season" in first-half stoppage time.
A rare handling error by Glover saw the Boro keeper spill a speculative effort from Enzo Fernandez into the path of Palmer, who volleyed the rebound high over the crossbar from five yards.
Despite his frustrating performance on Teesside, Palmer has arguably been Chelsea's best player this season.
He is the Blues' joint-top scorer with eight goals, while he has also provided seven assists - three more than any of his teammates.
Watch Cole Palmer's "Miss Of The Season" Against Middlesbrough
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