He said: "We have talked about the mistakes we made at Middlesbrough and the future. And the immediate future is playing Sunderland, trying to get three points and then waiting to see what happens with United.
"The title was difficult before; it is more difficult now. What we have to do is take our chances, and that is something that has been the same problem the whole season."
Fernando Torres will again be missing with an ankle injury while full-back Alvaro Arbeloa is out with a hamstring problem.
Benitez said: "We have to keep going. We are disappointed so we will try to win the next game and then have a week to plan for Real Madrid.
"We can still progress in the Champions League and it still gives us the chance of a trophy.
"We must keep going in the title race, to try to win each game as it comes along.
"Now we have the opportunity against Sunderland to do things right, to be able to approach the Real Madrid second leg with confidence. We have to remain positive.
"We have learned we must be more clinical, to finish games when you have chances.
"But we must not forget that our League performance is better than last season and we have had key players injured and maybe that could have cost us four or five points."
