John Buckley bagged a brace, with Jake Garrett, Sam Gallagher, Dilan Markanday, Zak Gilsenan, Tom Bloxham and James Edmondson also getting on the scoresheet at the EnviroVent Stadium.
Jon Dahl Tomasson made 10 changes from the side that beat Watford at the weekend, with only Dom Hyam retaining his place.
The Rovers boss has made it clear how much he values the cup competitions but admitted changes were inevitable due to the lack of options in several positions. Saturday’s trip to Plymouth will also have been in the back of Tomasson’s mind.
Leo Wahlstedt made his first appearance in a Rovers shirt after joining from Norwegian club Odds BK earlier this summer following Thomas Kaminski’s move to Premier League newcomers Luton.
Patrick Gamble made his competitive debut in an unfamiliar right-back role, while Scott Wharton partnered Hyam at the heart of defence.
Harry Pickering slotted in at left-back after missing the Watford trip through suspension, having been sent off against Hull a week prior.
Sondre Tronstad, Garrett and Buckley came into the midfield and Andy Moran made his first start. The Brighton youngster came off the bench at Vicarage Road after arriving in East Lancashire on a season-long loan.
Gallagher made his first start of the season after several promising cameos off the bench, with Markanday also coming into the side.
Tom Atcheson and Rhys Doherty, first and second-year scholars respectively, were both named on the bench for the first time in a competitive fixture.
Rovers were on the front foot from the first minute and looked slick in possession against their League Two opponents.
Gallagher was nearly played through on goal in the opening stages but Mark Oxley did well to rush out of his goal and get there first.
The opener came 10 minutes into the first half when Garrett found the bottom corner with a clinical drive across goal.
Gallagher doubled the lead moments later, latching onto Buckley’s ball over the top and keeping his cool to slot past Oxley.
Harrogate had a chance to pull one back at the other end but Wahlstedt made a smart stop to deny Jack Muldoon after a defensive mix-up.
The Swedish goalkeeper looked comfortable during his first taste of English football, showing composure to pick out a team-mate on several occasions despite the hosts’ pressing.
Wahlstedt made another smart stop midway through the first half to tip the ball round his post, but the offside flag had already gone up.
Buckley added a third after the half-hour mark, firing home after some good work by Moran who managed to go round the goalkeeper and keep the chance alive.
Garrett and Buckley were both on target against Walsall in the opening round and continued to have joy in the competition.
Harrogate spurned another big opportunity to get one back. This time Muldoon had Wahlstedt beaten but his strike crept wide of the post after combining with Abraham Odoh.
Markanday added a fourth just before the break, drilling home from the edge of the area to cap off an emphatic first-half display. His strike might have taken a nick off a defender on the way in.
It was the first time Rovers had scored four goals in a half since a 5-1 victory against Carlisle in the same competition in August 2018.
Tomasson made a couple of changes at the break, with Hayden Carter and Gilsenan coming on in place of Hyam and Pickering.
Despite the changes, Rovers picked up where they left off in the second half. Gilsenan was immediately involved in the action but his strike was slightly too high after getting on the end of Garrett’s cut back.
Buckley then sent Oxley the wrong way from the penalty spot after Tronstad had been tripped by a defender in the box.
There were a few question marks over the midfielder’s future at Ewood Park after he was left out of the squad at Watford, but Tomasson made it clear in the build-up to the game that Buckley is still very much part of his plans.
Rovers made a couple more changes after the hour mark, with Gallagher and Moran making way for Bloxham and Edmondson.
Gallagher will benefit from the workout, having missed the first couple of games due to an injury picked up in pre-season.
Gilsenan added a sixth minutes after coming on, giving Oxley no chance with a stunning free kick after he was brought down just outside the box.
The former Barcelona and Liverpool prospect had a Man of the Match performance on his debut against Walsall and continues to show promising signs.
Bloxham also made an impact off the bench, curling home a seventh 20 minutes from time after finding a pocket of space in the box. It was a special moment for the youngster, who arrived from Tottenham Hotspur over the summer.
Edmondson also marked his senior debut with a goal, providing a cool finish to slot past the onrushing Oxley after he was played through on goal.
Atcheson was also handed a debut off the bench, coming on for the final 10 minutes in place of Gamble, who looked reliable despite being used on the right of the backline.
Gilsenan had a chance to double his tally after again managing to get in behind the Harrogate defence, but this time he was denied by the legs of Oxley.
The Harrogate goalkeeper made another good stop in the final five minutes as Edmondson tried to lift the ball over him.
Rovers’ Academy has had plenty of success stories in recent memory, and the future looks bright at Ewood Park.
Perhaps another cup run could be on the cards after last season’s memorable victories against Premier League opposition in Leicester and West Ham.
Tomasson’s men will now be aiming to build on their momentum when they continue their league campaign at Home Park this weekend. A run of three successive away games looked tough on paper but so far, things couldn’t have gone much better.