Despite beating Charlton with a gritty 1-0 victory on Saturday, McCarthy opted to make four changes.
And it worked a treat as three of them - Luke Hyam, Carlos Edwards and Frank Nouble - came up trumps to move Town just two points, and two places, away from the top six.
McCarthy said: "It is nice when it works. I wanted some fresh legs in the team after a really difficult game against Charlton.
"But we shouldn't be losing anything by making these changes - we should be gaining lots of energy.
"I have only really got 18 outfield players but the Christmas period requires real management."
Ipswich took the lead on four minutes with a rare goal from Hyam, the midfielder picking up a headed clearance by Tommy Spurr to coolly fire the ball low past Jake Kean.
The hosts shaded the half chances, before Blackburn equalised out of nothing on the half-hour mark.
Scott Dann's long clearance caught the home defence cold allowing Jordan Rhodes to run through and beyond the advanced Dean Gerken to roll in the equaliser.
It was Rhodes' 11th of the season and while Blackburn ended the first half on top, it was Ipswich who once again came out of the blocks quicker.
Stephen Hunt tricked his way into the Blackburn box before being stopped by Grant Hanley but Edwards had the simple task of firing home the rebound.
The points were made safe when Dann and Kean woefully failed to deal with Tyrone Mings' long ball and Nouble tackled the Blackburn keeper and tapped into the empty net.
Of his goalscorers, McCarthy added: "We have been trying to get goals from midfield and we got them today.
"Frank (Nouble) was better in the second half, but that is what he should be doing. He is a handful and a frightening prospect when he is bearing down on you."
Blackburn boss Gary Bowyer accused his players of being too nice after claiming his side "gifted" Ipswich their second-half goals.
Bowyer added: "We didn't start bad and DJ Campbell could have scored within a minute.
"We didn't defend their first goal well enough although I thought we were the better side before half-time and deserved our equaliser.
"But we gave them their second goal and their third and you can't do that. It is not as if we were cut open and they scored breathtaking goals.
"It is frustrating as we have kept five clean sheets at home. We have to find the mentality to do that away from home - and stop being so nice."