Portsmouth have confirmed the departure of manager Tony Adams "with immediate effect".
The struggling Barclays Premier League club lost 3-2 to Liverpool on Saturday after conceding two late goals, and the Fratton Park board have opted to remove Adams and first-team coach John Metgod.
The club's director of youth operations, former Nottingham Forest boss Paul Hart, has been installed as caretaker manager.
Former Arsenal and England captain Adams had only been in charge on the south coast since October 25 when he was named caretaker manager following the departure of Harry Redknapp.
Adams was then confirmed as Pompey boss on October 28.
However, a run of just two wins in 16 league games has seen the club slide down the table and they now lie just one point above the relegation zone. They were also knocked out of the FA Cup after a 2-0 home defeat to Coca-Cola Championship Swansea.
Their most recent form shows just two points have been gathered in a nine-game run.
A Portsmouth spokesman told official club website http://www.pompeyfc.co.uk: "This has been a very difficult decision and Tony has worked tirelessly to arrest the slump in form.
"He is rightfully highly-respected within the football world and played a major role in our FA Cup triumph last season. We would like to thank him and John and wish them well in the future.
"The owner and the board feel they have been as supportive as they can during a period where results have been poor. The team has played well but too many points have been dropped from winning positions.
"Notwithstanding the adverse economic conditions the board remains committed to the continued growth and development of the club for the future, building on its achievements of the last three years.
"The priority is for Portsmouth Football Club to remain in the top flight and we feel the appointment of a new manager will give us the best opportunity to enable us to do this.
"Paul Hart knows the football club, having joined us nearly two years ago, and is a respected coach with managerial experience."
Today's announcement came despite Portsmouth chief executive Peter Storrie using his programme notes on Saturday to insist Adams' job was not in danger.
Speaking after the defeat to Liverpool, Adams appeared convinced he would remain in charge.
Adams said: "At the moment everyone is saying they want me to do the job, so I'll get on with it.
"We've got 13 games to go and have to play the teams around us. March on."
Portsmouth's owner Alexandre Gaydamak is known to be ready to sell the club and in December stated he could "no longer invest the time required to oversee the running of the club".
Preserving Portsmouth's top-flight status is a clear priority, and would ensure the club retains its worth to potential investors.
Former Chelsea manager Avram Grant, who prior to his stint at Stamford Bridge worked at Portsmouth as technical director, has this morning been linked with a return to the club.
Former Charlton manager Alan Curbishley has also been suggested as a possible successor to 42-year-old Adams.
The Portsmouth job was Adams' first frontline managerial post in the Premier League, however he had a spell in charge at Wycombe from November 2003 to November 2004, and later developed his coaching knowledge on the staff at Feyenoord and Utrecht in Holland.
Adams steered Portsmouth to just two league wins, against Sunderland and Blackburn, and saw star players Jermain Defoe and Lassana Diarra leave the club in big-money transfers.
Portsmouth's next match sees Manchester City visit Fratton Park on Saturday.
Former Portsmouth striker and player-manager Steve Claridge claimed Adams should have been given more time to turn things around.
Claridge felt Adams deserved "two or three weeks more" to give time for his January signings to settle in.
"I would have liked him to be given more time to see how those new players bed," he told Setanta Sports News.
"He's made mistakes, no doubt about it. One or two performances haven't been too bad but it's all about results. But there have been some terrible individual errors in recent weeks."
But Claridge admitted he understood the club's decision in the wake of their poor recent form.
He added: "I understand the decision. They're one of the teams in freefall. They're one of five clubs that, at this stage, look likely to go down. It's tough times."