Milan have not won the scudetto since 2004 and despite European Cup triumphs in 2003 and 2007, Ancelotti's position is looking increasingly precarious.
The Rossoneri only finished fifth last term and his cautious tactics this season have been criticised by fans and the media.
"The championship is not over. Inter have the chance to maintain their advantage but we must resist," he told reporters before later adding a note of realism.
"It is difficult. It is important to keep ourselves in the top three and then we will see."
Ancelotti, Serie A's longest serving coach having been appointed in 2001, said this week he would not leave for Chelsea in June but media reports have speculated he could be sacked by Milan in any case if they fail to win the title.
"I have a contract until 2010, after that we will see what to do," he said.
Inter's sheer power was the key to their victory and they ripped holes in Milan's shaky defence, which included 40-year-old Paolo Maldini in his last derby before retiring at the end of the season.
However, Adriano did use an arm for Inter's opener before Dejan Stankovic found space in the box to fire home. "I don't know if it was voluntary or not but the foul by Adriano was crucial," Ancelotti said. "On the second goal it was clearly a mistake on our part."
Inter coach Jose Mourinho, whose side are nine clear of second-placed Juventus and odds-on for a fourth straight scudetto, said the victory was deserved.
"It was an important win against a great side who put us under huge pressure at the end, which makes the win more special," he told a news conference before leaving without fielding questions.
"We wasted lots of chances to make it more secure."
