Petr Cech acknowledged mistakes on the pitch are not helping Andre Villas-Boas or his Chelsea players after the 3-1 defeat at Napoli.
Their defending for Ezequiel Lavezzi's double was far from impressive, and Cech said: "We know he (Villas-Boas) keeps working hard for us.
"He prepares every game with 100% commitment and we appreciate it as players, but if you have players on the pitch making mistakes he can't help it."
The Czech Republic international continued on Sky Sports: "I think it was an amazing game for the supporters to watch. There were a lot of counter-attacks, shots and chances, but if you come to a place where they are strong at scoring and leave them so many moments you can get punished.
"We went 1-0 up and had a spell where we controlled the game but they got a goal just before half-time that made a difference because they could sit back and wait for the counter-attack.
"We tried to score and it became dangerous for us as they looked for a third goal.
"When everything goes wrong you have a rebound like we did for the third goal. The bounce went in the perfect place for them.
"We always say we keep working hard on the training ground but unfortunately we don't seem to transport that that on the pitch.
"We have quality players who can turn it around but it could be better because we don't have time to recover. We have a lot of games coming up and we are not in a position to drop many points in league.
"It's not an ideal situation but we are still in the Champions League and we will fight to the end."
Mata put Chelsea 1-0 up before Lavezzi's double and an Edinson Cavani goal turned things around, making for a testing return at Stamford Bridge.
He said: "One-nil would have been an excellent result for us but we didn't keep it. Napoli are a very strong team in this stadium but now we have the second game and we are going to put in 100% at the Bridge.
"I knew it would be an open game because Napoli are offensive with three players - Cavani, Lavezzi and Hamsik - who are very fast on the counter-attack, but today we had a lot of chances to score and we will have to convert those chances at the Bridge.
"I have confidence in this team, we are not dead. It will not be easy for us but I think we can do it."
Villas-Boas was left rueing a missed chance and poor defending. Daniel Sturridge wasted a glorious opportunity to play in Mata for a second Chelsea goal, before Lavezzi was given space for the equaliser.
In the second half, David Luiz kicked a long ball straight against Cavani, who squared past the stranded Cech for Lavezzi to steer into an unguarded net.
The Chelsea boss said: "We had a chance to go 2-0 up and a couple of defensive mistakes that against Napoli, with their attacking strength, will get punished.
"A one-goal disadvantage would have been a bit better but it is not impossible to recover 3-1 because of the number of chances we get and the environment we must create to turn this tie around and go through.
"We will analyse strongly what we did wrongly because a couple of things need to get better. We have the knowledge we can create problems with our attacking options.
"In the end the statistics were similar, both teams created a lot, the game was open and end to end. Napoli scored their third goal in our best period and it took us a little bit down. Didier Drogba had a chance at the end - but there is a big possibility, with this away goal, to turn the tie around."
Asked about his team selection - he did not start with Frank Lampard, Michael Essien, Ashley Cole or Fernando Torres - Villas-Boas said: "You can have your opinion but it was based on what was the best team in my thoughts."
Asked if he believed if he would still be in charge for the second leg, the Portuguese added: "For sure."