Andre Villas-Boas today "parted company" with Chelsea, the club have confirmed.
The 34-year-old lost his job less than 24 hours after yesterday's Barclays Premier League defeat at West Brom, which left the Blues fifth in the table.
Chelsea also announced assistant manager Roberto Di Matteo would take charge of the team until the end of the season.
Villas-Boas was only appointed eight months ago and cost billionaire owner Roman Abramovich £13.3million to land from Porto.
Chelsea said in a statement on their official website, "Andre Villas-Boas has parted company with Chelsea Football Club today.
"The board would like to record our gratitude for his work and express our disappointment that the relationship has ended so early.
"Unfortunately the results and performances of the team have not been good enough and were showing no signs of improving at a key time in the season.
"The club is still competing in the latter stages of the UEFA Champions League and the FA Cup, as well as challenging for a top-four spot in the Premier League, and we aim to remain as competitive as possible on all fronts.
"With that in mind, we felt our only option was to make a change at this time.
"With immediate effect, Roberto Di Matteo has been appointed first-team coach on an interim basis until the end of the season."
Di Matteo's appointment on a caretaker basis ended speculation Rafael Benitez would be parachuted into Stamford Bridge until the summer.
Villas-Boas had been under mounting pressure after overseeing what was threatening to be Chelsea's worst season since Abramovich bought the club almost nine years ago.
A run of just five wins from the last 16 games saw the Blues slide out of the top four, while they remain in real danger of crashing out of both the Champions League and FA Cup in the next week and a half.
Brought in to revamp an ageing squad after winning an incredible quadruple at Porto last season, Villas-Boas' reign was dogged by reports of the kind of dressing-room unrest that previous Chelsea managers have said led to their own downfall.