Javier Hernandez put United ahead after just 36 seconds at Old Trafford and Nemanja Vidic then doubled the hosts' advantage; Frank Lampard's late goal gave Chelsea brief hope, but Ancelotti feels they had already allowed their title hopes to slip through their fingers.
"In the first minute, we lost the game," he told Sky Sports. "We started so badly. It was very difficult after that to come back and try to win. The second half was better but United played better and deserved to win.
"We have to accept the defeat. Today, United were better and, in general this season, they were better than us. They deserve to win the title. They will win and we have to try to maintain second place."
David Luiz was culpable for the first goal and was replaced at half-time, but Ancelotti said the substitution was down to an injury problem he had sustained on Saturday.
"He had a little problem yesterday in training," he said. "We tried this morning and he said it was okay so I put him on the pitch. On the pitch, you can make a mistake."
Talk remains rife that Ancelotti will be on his way out of Stamford Bridge this summer, but he remains hopeful that he will be given another chance despite ending the season without silverware.
"We have to wait two weeks - it is not a long time," he said. "I hope to stay but it is not my decision."
Asked whether he would welcome a return to Italy if he lost his job, he said: "Italy is my country and I cannot say I don't want to come back to Italy - I will come back to Italy one day as I love my country.
"But in the last two years I have found a fantastic atmosphere in football, a fantastic country, and I respect the people. There is no violence in the stadium, the stadiums are full and I would like to stay here for these reasons."