A 2-0 defeat at Manchester City on Sunday afternoon dented the London club's hopes of finishing second and they are now looking over their shoulders.
Tottenham Hotspur could move third with a win over West Ham United on Monday night, while Arsenal are just two points behind Chelsea.
And Benitez told Sky Sports of the race for the top four after the loss to City: "I said before the game, (if we win) it will still be a battle to the end.
"Not winning is exactly the same situation. We have to carry on until the end."
A penalty save from Joe Hart against Frank Lampard after the goalkeeper had brought down Demba Ba set the platform for City's win.
Yaya Toure and Carlos Tevez went on to score the goals to settle the game but Benitez thought the spot-kick was a turning point.
"The penalty is a crucial moment," he said. "We did not do as well as we were expecting but the penalty could have changed everything.
"It was a good penalty and a good save. Ten minutes later, they score. Then we have to take a risk and it is clear they are a good team."