Trailing 3-1, Liverpool will need to score at least as many goals as they did in Istanbul in 90 minutes at Stamford Bridge; still no easy task as Benitez was forced to admit.
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'I was disappointed with the manner of our defeat, and the bad mistakes we made at set pieces to allow them two goals,' said Benitez.
'Now it will be very difficult. We have to score three times at Stamford Bridge, which is a tough call against a very good side.
'Our first priority, though, is against Blackburn in the league, then we will see what we have to do at Chelsea.'
Fernando Torres put Liverpool ahead early on, but two headers from set pieces by Branislav Ivanovic put Chelsea in control, with Didier Drogba snatching a third.
Benitez said: 'We scored first but after that we were never in control. We conceded a bad equaliser from a set-piece. That was not because of the zonal marking but because players made mistakes to allow people space and time.
'For their first goal there were three players near to the scorer and they were not able to stop him. And then something very similar happened for the second, we made bad mistakes at crucial times.
'Now we know we have a difficult task in the second-leg. We have to score three times and that will be very difficult.
'But we must believe we can do it. We have scored four at Manchester United so we know what we are capable of.
'Chelsea did not really surprise us, and they clearly believe that this is the competition they have most chance of winning now.
'They have won many away games this season, but the way we lost was hard to take.'
Benitez's opposite number, Guus Hiddink, was understandably elated to have come out on top in his first meeting with Liverpool as Chelsea manager hailed his team.
'I admit it was an unexpected result, but we are very happy with the win and it was well deserved,' said the Dutchman.
'We started very sloppily, the jobs we were doing in defence were not as good as they could have been.
'We let them score far too easily, but I can only compliment my team for their recovery from that setback. Straight afterwards we could have equalised on two occasions.
'But we reacted well, we scored with a very good set-piece and from then on the confidence flooded through our team.
'We pinpointed areas in our opponents' side where we could hurt them. The team could smell that and they took advantage. We talked about that situation again at the break and made sure we continued in the same way.'