An own goal by Sweden defender Pontus Jansson put Chelsea ahead before Jorginho’s penalty ensured their first semi-final in the competition for three years
With his selection plans disrupted by Covid-19 and injuries, Chelsea boss Tuchel gave debuts to three teenagers including 18-year-old Harvey Vale, who headed his side’s best chance of the first half straight at the keeper.
But it was Brentford who carved out the better openings before half-time and Kepa Arrizabalaga marked his rare start in goal with three fine saves to deny Yoane Wissa, Mathias Jensen and Rico Henry.
Henry almost scored an own goal at the other end before Jansson inadvertently sliced Reece James’ cross past Alvaro Fernandez in the 80th minute.
Substitute Jorginho doubled the lead five minutes later after Fernandez brought down Christian Pulisic.