Rovers boss Mark Hughes made two changes to the side that lost 3-0 to Portsmouth on the opening day. The suspended Lucas Neill was replaced by Zurab Khizanishvili, while Brett Emerton was preferred to Aaron Mokoena at right-back.
Everton manager David Moyes made three changes to the side that defeated Watford at the weekend, Kevin Kilbane, Leon Osman and Gary Naysmith coming in for Simon Davies, Cahill and the injured Nuno Valente.
The introduction of new signing Andre Ooijer got the Ewood Park crowd going just moments before kick-off and they were almost celebrating a goal just two minutes after referee Uriah Rennie blew his whistle.
After good work down the right between Andy Todd and Emerton, David Bentley slipped the perfect throughball for Jason Roberts but, after forcing himself wide, the former Wigan man was denied by Tim Howard low at his near post.
Just before the quarter hour, Rovers twice went close in the space of a minute. McCarthy volleyed over after a Morten Gamst Pedersen header had picked him out at the back post, before Roberts again found himself clean through but, after cutting inside onto his left foot, he blazed wide of the goal with men spare to his left.
The closing stages to a stop-start half, which brought a string of bookings for Mikel Arteta, Pedersen, Todd and Bentley, again saw Rovers go close. Michael Gray's ball over the top found Bentley in space and, after taking the keeper out of the equation with a ball to his left, only a last-ditch Joseph Yobo tackle prevented a certain McCarthy goal.
But just five minutes after the break, the South African had his goal. The former FC Porto striker started the move, finding Bentley in space and, after Yobo's tentative tackle halted his run, McCarthy collected the loose ball and expertly picked out the bottom corner with a curling right-foot shot.
The goal spurred Moyes into a double substitution, with Cahill and James McFadden replacing Kilbane and James Beattie, and it ultimately paid dividends.
Both sides had their chances before the goal arrived however, with Roberts again denied by Howard from point-blank range, before Brad Friedel proved just why he is one of the best keepers around in a one-on-one situation, saving Andy Johnson's effort with his legs.
But with just six minutes remaining, Everton's pressure told with the equalising goal. McFadden latched on to a ball over the defence and, after lifting it over Friedel and onto the post, Cahill was on hand to tap home the rebound from 10 yards out.