The Tractor Boys have picked up 16 points out of a possible 24 since the former Wolves manager arrived at Portman Road, and Saturday's victory over Millwall saw the club keep a clean sheet for only the third time this campaign.
Cresswell believes the clean sheet was thanks to his new manager selecting a settled defence.
McCarthy has named Cresswell at left-back alongside Bradley Orr, Luke Chambers and Tommy Smith for the last three games and Ipswich have won all three and conceded just twice.
In the three games before that, Town conceded eight and won just once.
"We've had the same back five for a while now and I think we've looked pretty solid," he told the club's official website.
"Obviously we know that we have to keep performing well, as we've got players waiting in the wings to break into the side, but I think it's healthy to have competition for places.
"When a new manager comes in, it can be a difficult time. They come in with their own philosophies and ideas for how they want to play and it's up to the players to adapt to that and earn their place in the starting line-up.
"The gaffer has been pretty straight with us since he took over and we've had a settled back-line for some time now.
"I think that is helping us as a team and we are all enjoying our football at the moment."