Fulham boss Mark Hughes claims Dempsey's penalty should have been retaken, suggesting referee Mike Dean knew as much.
"Drogba was encroaching in the box," he said.
"Mike Dean saw it: he was alongside Clint as he kicked it. Mike Dean saw that, so it should have been retaken."
Cech's save denied Fulham a sixth straight home win and only their second derby victory over Chelsea in 29 attempts.
Hughes added: "Given the circumstances at the end, it's disappointment.
"We came up against a strong Chelsea side who posed questions of us in the second half, and we had to be strong and resilient.
"But it was a real opportunity to beat a very good side at the end.
"We've been playing well of late and showed real character to dig in and create chances at the other end."
Hughes was not surprised by Ancelotti's decision to axe one of Drogba or Torres.
"We sensed there might be a change," said Hughes, who revealed Cottagers defender Brede Hangeland played despite suffering from "a raging temperature" during the afternoon.
"The talk was about rotation leading up to the game, different systems, so we thought one of them might start from the bench.
"They've got big games coming up.
"Maybe Carlo thought this would be a good game for Fernando to start."