Sunderland have sacked boss Steve Bruce following a torrid run of results.
Bruce, 50, becomes the first Premier League boss to lose his job this season after two wins in the first 13 games.
"It is my job to act in the best interests of our football club and I can assure everyone that this is not a decision that I have taken lightly," said chairman Ellis Short.
"Sadly results this season have simply not been good enough and I feel the time is right to make a change."
Assistant manager Eric Black will take charge of first team duties as the club searches for a new manager.
Bookmakers have installed former Aston Villa boss Martin O'Neill as the early favourite to replace the ex-Manchester United defender, with Mark Hughes, Rafa Benitez and Guus Hiddink also figuring prominently in the betting.
Bruce joined the Black Cats from Wigan Athletic in the summer of 2009 and led the club to a 10th place finish in the Premier League last season.
However, the Stadium of Light side were sixth at the end of January after opening the year with three wins and one draw.
They then sold striker Darren Bent to Aston Villa in a deal which could rise to £24m and results took a turn for the worse.
The team struggled to score goals and matters were compounded when £13m signing Asamoah Gyan left the club in September - Bruce claiming "parasites" turned Gyan's head after his goal in the 1-1 draw with England at Wembley in March.
Bruce brought in a raft of new signings over the summer, but the Black Cats have slumped to within two points of the relegation zone this season, and Short acted quickly to stop the rot.
"Steve has acted with honesty and integrity throughout, which is testament to the character and commitment he has shown during his time at Sunderland," Short added.
"I would like to personally place on record my thanks to him for his significant contribution to our football club over the past two and a half years and everyone here at Sunderland naturally wishes him the very best for the future.
"I would also like to thank our fans, who have endured a trying start to the season. Their support continues to be the driving force behind our club and is vital as we now look to the future."
Speaking to BBC Radio 5 live, former Sunderland striker Kevin Phillips believes the players should take some of the blame for Bruce's dismissal.
"At the end of the day the players need to look at themselves," he said. "Steve has brought in a lot of players for a lot of money and they haven't responded for him.
"The fans have got frustrated and taken that out on Steve and ultimately it is the manager who always pays the price."
Bruce started his managerial career at Sheffield United in 1998 before spells with Huddersfield Town, Wigan Athletic (twice), Crystal Palace and Birmingham City.
In 98 games in charge of Sunderland, his team won 29 matches, drew 28 and lost 41.
Former Sunderland defender Michael Gray told BBC Radio 5 live: "Go back to the summer and Sunderland brought in 10 new players, and we kept saying week after week the players are still gelling. But how long do you need?
"We are 13 games into the Premier League and everybody's expectations were for the top 10 this season and we are nowhere near that.
"Somebody else is going to take the reins but they need to get us looking up the table rather than looking down."