Cameron Humphreys netted just before the break to give the Blues a 1-0 half-time lead over Rotherham United in their FA Cup third round tie at Portman Road.
Town boss Kieran McKenna made eight changes from the team which drew 1-1 at Lincoln on Monday.
Vaclav Hladky was in goal with Kane Vincent-Young, Richard Keogh and George Edmundson, who missed the trip to Lincoln on Monday as he was unwell, at the back.
Leif Davis, who was also too ill to travel to Sincil Bank, was on the left with Kayden Jackson wide on the right. In central midfield, Lee Evans skippered alongside Humphreys.
Sone Aluko and Conor Chaplin were the number 10s behind Freddie Ladapo, facing his old club.
New signing Massimo Luongo was on the nine-man bench alongside third-choice keeper Joel Coleman, Sam Morsy, Wes Burns, Kyle Edwards, Marcus Harness, Greg Leigh, Cameron Burgess and Gassan Ahadme. Neither Janoi Donacien nor Luke Woolfenden were in the squad.
Championship Rotherham named only seven subs due to injuries and loan players returning to their parent clubs.
The Blues were first to threaten in the fourth minute when a Davis corner from the left found Chaplin at the near post but Town’s 12-goal top scorer turned his shot wide.
A minute later, Jackson was sent away on the right but screwed his attempt at a cross into the stand behind the goal.
Town continued to look the side most likely to claim an early goal and in the seventh minute, Chaplin sent over a ball from the left to Jackson beyond the far post but the former Barnsley man was unable to direct his effort towards goal on the stretch.
The Millers had the ball in the net in the ninth minute but their fans’ celebrations were short-lived, the linesman raising his flag after Shane Ferguson had crossed low to one-time Town target Conor Washington, who tapped home from close range, but having strayed offside.
On 14, after a corner had been cleared, Vincent-Young played the ball wide to Aluko, who cut inside from the left and hit a shot across Rotherham keeper Viktor Johansson, who batted the ball away from goal.
Five minutes later, with Town still well on top and well in charge, Aluko struck a shot from the right of the box wide of goal.
In the 28th minute, Ferguson struck a low effort from distance which Hladky claimed down to his left.
The Blues went close again as the game move to the half-hour mark, the ball dropping to Chaplin inside the area following a Humphreys cross from the left and the forward hitting a powerful effort which Johansson parried away to his left.
In the 41st minute, Humphreys and Ladapo’s pressing saw Town regain the ball 10 yards outside the Millers’ area and Jackson hit a shot which deflected through to Johansson.
And three minutes later, Town made their superiority tell when they took the lead. Jackson won the ball on the right before feeding Ladapo, who played a return ball in to his path as he broke down the flank. Jackson cut back and Humphreys arrived on the edge of the area to hit a low shot beyond Johansson to his right and inside the post to claim his third goal of the season and his first in the FA Cup.
The Blues went in at half-time deservedly in front having controlled the game throughout and having been much the better side, creating a number of chances prior to going in front, while Hladky had been untested
Town: Hladky, Vincent-Young, Keogh, Edmundson, Davis, Evans (c), Humphreys, Jackson, Aluko, Chaplin, Ladapo. Subs: Coleman, Burgess, Leigh, Luongo, Morsy, Burns, Edwards, Harness, Ahadme.
Rotherham: Johansson, Harding, Wood (c), Humphreys, Kioso, Odoffin, Rathbone, Lindsay, Bramall, Ferguson, Washington. Subs: Hemfrey, McCart, Douglas, Bola, Barlaser, Warne, Ogbene. Referee: Sebastian Stockbridge (Tyne and Wear).