Hayden Hackney's close-range strike secured a slender first-leg advantage for Middlesbrough in the Carabao Cup semi-final.
Hackney gave the Championship side a shock lead against run of play in the first-half on Tuesday night.
Isaiah Jones' cross was slotted home from six yards out by the late-arriving Hackney.
Cole Palmer missed a sitter as Chelsea spurned several gilt-edged chances.
More to follow
Midfielder Hayden Hackney (centre) put Middlesbrough ahead in the 37th minute
Isaiah Jones' cross was slotted home from six yards out by the late-arriving Hackney
Cole Palmer missed a sitter for Chelsea in the first-half against Middlesbrough
Palmer fired over the bar with the goal gaping after Tom Glover spilled Enzo Fernandez's shot
The home side were forced to make a change when Alex Bangura was forced off by injury
Middlesbrough striker Emmanuel Latte Lath went off after being caught by Axel Disasi