Chelsea have won their last three Premier League matches and kept four clean sheets since Benitez took over last month following the sacking of Roberto Di Matteo.
"We look more organised. We were conceding far too many goals and we were too open," Cech told the club website.
"We've been defending much better as a team and that's been the key, because we weren't defending well.
"We are back to being difficult to score against, which is a big help, and of course we have quality players who can score goals."
Chelsea have conceded eight times in Benitez's 10 matches in charge, compared to 21 in the same number of games at the end of Di Matteo's tenure.
"You need the whole team to defend. We have very attack-minded players and sometimes we weren't making the right choices in terms of defensive transitions, we are pressing the ball much better now so it gives us more time to re-organise, I think that's been the most significant change," added Cech, who will make his 400th appearance for Chelsea against Everton on Sunday.