In what some might construe as the beginning of the managerial mind games for the Barclays Premier League run-in, Ancelotti reiterated his own side needed to win their nine remaining matches to stand any chance of completing one of the great title comebacks.
But the Italian also claimed any further mistakes by United and Arsenal would see the top two pay the ultimate price and miss out on the championship.
Head-to-head: Ancelotti has warned Manchester United his Chelsea side are ready to pounce on any slips at the top of the table
'To make a mistake now is very dangerous,' said Ancelotti, whose side will take to the field at Stoke on Saturday afternoon looking to pounce on any United slip-up at West Ham.
'Make a mistake here you can lose your possibility to win something.
'It's not just for us. Also Manchester United, also Arsenal. They cannot make a mistake either.'
Chelsea are nine points behind United with a game in hand and four adrift of Arsenal.The champions retaining their title looked unthinkable a month ago as they languished 15 points off top spot.
But a perfect March, which co-incided with a serious blip by their rivals, resurrected their hopes ahead of what will be a season-defining month. And on May 8 they have to visit Old Trafford in the Premier League.
'Always, in April, at the end of the season, you have to play calmly,' said Ancelotti, whose side also take on United in the Champions League quarter-finals over the next 12 days.
'For me, we are ready to play.Three months ago, November or December, it would have felt like a dream to arrive in this situation now.
Best of both: Ancelotti admits he has different uses for Torres and Drogba
'I don't know what we will achieve in the end, but we have a possibility to fight.
'Maybe tomorrow we'll lose the game, but my idea is the team have a good sensation.'
The fact Chelsea have managed to haul themselves back into the title race is all the more astonishing considering their strikers have failed to score in the league since Fernando Torres was signed two months ago.
'Fortunately, we didn't need their goals,' said Ancelotti, who must know deep down that winning the last nine league games will be impossible unless Torres, Didier Drogba, Nicolas Anelka or Salomon Kalou start finding the net.
'In April, they'll come back to score. You can't lose that ability.
'If you are a top scorer, you'll stay like that until the end of your career.'
It could be argued Ancelotti rotating his strikers has not helped any of them end their droughts.But the Chelsea boss revealed he would persist with the policy and insisted he did not have a preferred forward partnership.
'The choices I make on it are down to the players' physical condition and the tactics,' he said, declining to reveal who he had in mind for a Stoke team he refused to underestimate.
Respect the ref: Ancelotti says he does not need to remind his players of their responsibilities on the pitch
'If we want to play on the counter-attack, we'll use Anelka and Torres, players who can move quickly in front.
'When we need more power, we'll use Drogba.'
Whatever happens in the title run-in, Chelsea would never resort to undermining referees, according to Ancelotti.
The Premier League are planning a crackdown on the lack of respect they believe managers and players show officials.
Ancelotti admitted his Chelsea squad do not show him much respect when he officiates their training matches but insisted they know not to cross the line when it comes to match day.
'I try to ref every day here and there is a lot of shouting against the referee,' he said.
'If you think it is a problem in the Premier League, you should look at other games and other leagues. It's worse in Italy.
'I don't tell my players they have to respect the referees because they know that.
'They know they have to respect the officials and their opponents. That's maybe the first rule of football.'
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Explore more:People: Fernando Torres, Nicolas Anelka, Didier Drogba, Carlo Ancelotti Places: Italy