Russian owner Roman Abramovich displayed his trademark ruthless side by sacking Di Matteo following an emergency, middle-of-the-night executive meeting at Chelsea's training ground, which came after a 3-0 loss at Juventus in the Champions League.
That result left Chelsea's defence of the European trophy in tatters, with the team on the verge of becoming the first reigning champion to be eliminated from the group stage. Chelsea has also dropped to third place in the Premier League after picking up just two points from its last four matches.
"The team's recent performances and results have not been good enough and the owner and the board felt that a change was necessary now to keep the club moving in the right direction as we head into a vitally important part of the season," Chelsea said in a statement.
There was no immediate announcement on a replacement for Di Matteo but former Liverpool manager Rafa Benitez is the favourite with British bookmakers, having already declared his interest in the role. Benitez, who was flying to London from Abu Dhabi on Wednesday for talks with Chelsea, has been out of work since being fired by Inter Milan in December 2010.
Pep Guardiola, currently on a one-year sabbatical from coaching after leaving Barcelona at the end of last season, is also a contender, along with Harry Redknapp and one-time interim Chelsea manager Avram Grant.
"The club will be making an announcement shortly regarding a new first-team manager," said the statement, with Chelsea not saying whether the appointment will be permanent or temporary.
Given Abramovich's history of hastily firing managers — he is looking for his ninth in nine years — there was a certain inevitability about Di Matteo's demise, even though the Swiss-born Italian was only hired on a full-time basis in June after an impressive spell as caretaker coach.
Di Matteo was told by chairman Bruce Buck and chief executive Ron Gourlay that he had been fired at the 4 a.m. training-ground meeting, soon after landing back in England following a flight from Turin. He is believed to have already said farewell to his players in the dressing room after the loss to Juventus.
"Wow, Chelsea have sacked their manager!! ... its a madness," Manchester United defender Rio Ferdinand said on Twitter.
Chelsea was in disarray when Di Matteo, then an assistant coach, took over from the fired Andre Villas-Boas in March. The former Italy midfielder brought together squabbling factions within the squad and led the team to the FA Cup title — the club's seventh — and then a first Champions League trophy, beating Barcelona in the semifinals and then Bayern Munich in the final.
Di Matteo, with his typical coolness, has also been praised for the way he handled a racism case involving John Terry that engulfed the club. Chelsea is in the middle of another racism incident, having accused a Premier League referee of abusing one of its players.
Abramovich moved quickly and mercilessly following the team's first disappointing run of results this season.
"It's been a difficult day," Chelsea playmaker Juan Mata said on his Facebook page. "I would like to thank him for all this time with us and wish him the best of luck for the future."
In the Premier League, Chelsea had been leading for much of the season but now trails Manchester City and Manchester United in the title race.
The team is third in Group E of the Champions League behind Shakhtar Donetsk and Juventus with one match left. The Blues next face Danish club FC Nordsjaelland, but they will be eliminated even if they win if Juventus earns at least a point in Ukraine.
"The club faces a difficult task ahead in qualifying for the knockout stages of the UEFA Champions League as well as maintaining a strong challenge for the top of the Premier League while competing in three other cup competitions. Our aim is to remain as competitive as possible and challenge strongly on all fronts," Chelsea said.
If a replacement is appointed before this weekend, as expected, he faces a tough start his tenure — Chelsea's next game is at home to unbeaten Man City, the defending champion, on Sunday.
In Benitez's favour is his experience — he won the Champions League with Liverpool in 2005 — and his close relationship with Fernando Torres from their time together at Anfield. Getting the best out of Torres could be crucial to pleasing Abramovich, who signed the Spain striker for 50 million pounds ($81 million) in January 2011.
Hiring Benitez would raise eyebrows, however, given his trademark defensive approach. Abramovich is widely known to prefer his team to show a more attacking style, demonstrating this by spending a combined reported 70 million pounds ($110 million) on attacking midfielders Oscar, Eden Hazard, Marko Marin and Victor Moses in the off-season.
Guardiola, the architect behind Barcelona's stunning recent success, is believed to be Abramovich's preferred choice. In four years at the Nou Camp, he won three Spanish league titles and the Champions League twice while retaining the team's attractive passing style so admired by Abramovich.
AP Sports Writer Chris Lehourites contributed to this report.