Marcus Harness has scored twice and Greg Leigh once to give the Blues a 3-0 half-time lead against Northampton Town at Portman Road in the Papa Johns Trophy.
Dominic Ball and Richard Keogh were handed their expected debuts as Blues boss Kieran McKenna made 11 changes.
Vaclav Hladky was in goal with Keogh in a two-man backline alongside Cameron Burgess with Kane Vincent-Young at right-back and Greg Leigh on the left.
Ball joined Cameron Humphreys in the centre of midfield with Kyle Edwards and Harness either side of stand-in skipper Sone Aluko behind lone central striker Kayden Jackson.
Nick Hayes was the sub keeper, while U21s captain Fraser Alexander was also on the bench.
As the game kicked-off, Town announced Zanda Siziba was replacing Conor Chaplin among the subs, the forward having picked up a niggle in the warm-up.
Northampton made six changes from the team which lost 1-0 at home to Doncaster at the weekend. Akin Odimayo was handed his full debut, while Josh Eppiah missed out having not been ready to return.
Town created their first chance in the seventh minute when Edwards picked up a loose pass on the right and drove forward before playing forward to Jackson, who was flagged offside as he hit his shot against Cobblers’ keeper Jonny Maxted.
The Blues subsequently began to take control with crosses flying in from both flanks in the following attack but with the ball just not falling for a Town player.
Town kept up the pressure and in the 11th minute went in front. A flowing move from just outside their own box in which Aluko and Edwards exchanged passes on a number of occasions, ended with the former West Brom man lifting a cross towards the far post where Harness got above Harvey Lintott - who really ought to have done much better - before nodding back across goal and over the line off the underside of the bar and the inside of the post.
The Blues went looking for a second and on 16 Edwards brought the ball across the area before hitting a powerful left-foot shot which Maxted did well to push over the bar.
And from the corner, Town and Harness scored their second. The flag-kick was taken short to Aluko, who brought it to the byline before laying it back to Harness, whose initial shot was blocked.
The ball ran loose and Ball looked to be fouled as he sought to shoot goalwards but before referee Tom Reeves could make a decision, Harness had stabbed it between the keeper’s legs over the line for his second of the game and fifth of the season, although he, like most at Portman Road on Saturday, will feel it should have been the sixth.
On 20 Northampton’s Kieron Bowie shot low past Hladky’s left post but it was still mainly Town and three minutes later Jackson rounded Maxted but took the ball too wide and was unable to find Harness with his low cross.
But the sparse crowd didn’t have to wait too long for a third with Greg Leigh this time the man on target. Edwards was again the creator, chipping another cross to the far post from where Leigh outmuscled Lintott and headed in his first goal for the club from the narrowest of angles.
Town continued to dominate and went looking for a fourth. On 34 Edwards worked the ball in from the right exchanging passes with Vincent-Young and Harness before striking a shot which was blocked.
The Blues lost skipper Aluko to injury in the 39th minute when the former Nigerian international picked up what looked to be a knee injury after falling awkwardly following a challenge. He immediately looked in pain and after treatment was clearly unable to continue and was helped to the tunnel by two members of the club’s medical team.
Late replacement sub Siziba took over, making his fourth appearance from the bench in the competition in addition to one start. On 44 Ball picked up a debut booking for a pull just inside the Town half.
The injury stalled Town’s momentum in the final minutes of a half they had controlled from start to finish.
As they had in the Carabao Cup tie against Colchester earlier this month the Blues’ fringe players had created early opportunities but on this occasion had taken one with Harness scoring when he looked very much second best to win the ball.
The former Pompey man showed his predatory instincts to add the second, then Leigh also won a header he shouldn’t have done to add the third.
The only downside was the concerning-looking injury suffered by Aluko and the knock Chaplin picked up in the warm-up.
Town: Hladky, Vincent-Young, Keogh, Burgess, Edwards, Ball, Humphreys, Leigh, Aluko (Siziba 42) (c), Harness, Jackson. Subs: Hayes, Edmundson, Morsy, Alexander, John-Jules, Ladapo.
Northampton: Maxted, Fox, Appere, Hylton, Pinnock, McWilliams (c), Bowie, Lintott, Odimayo, Haynes, Dyche. Subs: Leonard, Koiki, Tomlinson, Abimbola, Ngwa, Cross, Dadge. Referee: Tom Reeves (Birmingham).