Two Shefki Kuqi goals either side of half-time gave the Blues their first away win of the season at Rotherham. The home side rarely threatened as Town cantered to third place in the Championship table.
Town lined-up as expected with Fabian Wilnis recovering sufficiently from his shin injury to play at left-back. Jim Magilton made his first league start of the season in a four-man midfield, Premiership target Darren Bent and Shefki Kuqi starting up front.
The Millers started brightly and in the second minute Paul Shaw's shot from the left of the area deflected wide off Jason De Vos.
Four minutes later, Kelvin Davis blocked in front of Michael Proctor after a ball had been chipped into the area ahead of the former Sunderland frontman.
Kevin Horlock put Town's first shot of the game over the bar in the 13th minute, after a long Darren Bent run up pitch.
Shefki Kuqi headed a Diallo cross wide, before former Blue Chris Swailes became the first man to pick up a yellow card, for a foul on Jim Magilton.
Chris Sedgwick, a scorer in the corresponding fixture last season, struck a shot wide off De Vos as he sought to repeat the feat. Not long after, John Mullin saw yellow for a tackle from behind on Tommy Miller.
On 42, Kuqi struck a powerful shot straight at Rotherham keeper Mike Pollitt, but a minute later the Finnish international did break the deadlock.
The striker seized on a loose ball around 30 yards out to the left of goal and crashed a first time shot into the far corner of Pollitt's goal, the keeper virtually stationary on his line. It was a terrific finish and an early contender for the Town goal of the season.
The goal sent Town fans off for their half-time coffees with a spring in their step, the Blues having weathered some early pressure from the Millers. However, as the half had worn on Town had gradually gained control.
The second half was only a 90 seconds old when Kuqi put the Blues further in front. Bent showed Kuqi-like persistence first to keep the ball in play and then to stab a foot in-between Phil Gilchrist and Mike Pollitt, the ball rolling across the six-yard box for Kuqi to tap into the empty net.
From there the result was never in doubt. Town passed the ball around as well as they have this season, the performance streets ahead of the rather dismal displays at Nottingham Forest and Derby.
Davis made a decent left-handed save from Richie Barker's edge of the area shot but the home side created little problems for the Town defence.
Richard Naylor was somewhat harshly booked for handling the ball on 53 and then came close to winning a freekick on the edge of the Rotherham box. The Town central defender appeared to be fouled by Rob Scott as he turned him, the referee deciding it had been a fair challenge.
Just after the hour, Millers' midfielder John Mullin ought to have been shown a red card for an awful studs high on Ian Westlake's thigh. The youngster looked to be in some pain as Fabian Wilnis remonstrated with Mullin over the tackle.
The challenge looked like it warranted at least a second yellow card but surprisingly referee Graham Laws chose to speak briefly to Wilnis but failed to even call Mullin over for a chat. Fortunately, Westlake was OK to continue.
Town annoyance at that decision was compounded in the 69th minute when Jason De Vos was booked for an innocuous foul on Barker. Soon after, Dean Bowditch replaced Darren Bent in the Town attack.
Kelvin Davis saved a shot from former Town loanee Paolo Vernazza in the 73rd minute and Mike Pollitt did well to save Ian Westlake's strike from Tommy Miller's ball across the box.
With 14 minutes remaining, it looked like Kuqi might grab his hat-trick but his flicked header from Bowditch's cross flew past Pollitt's post. Tony Dinning replaced Jim Magilton who was given a terrific ovation as he left the field by the Town support.
Late on, Bowditch's deflected shot was easy for Pollitt, Davis similarly comfortable with Proctor's effort at the other end.
A comfortable win for Town against a Rotherham side which threatened little once the Blues had gone ahead. An early flurry of corners aside, Town enjoyed control of game throughout.
After the second goal Town were happy to sit back on their lead and gained their second clean sheet of the season (the first in the league) with little of the panic seen on previous visits to Millmoor.
The defence looked solid throughout with Naylor continuing to look increasingly comfortable alongside Jason De Vos. Diallo put in his usual solid defensive display, his aerial ability particularly noticeable at Rotherham corners, but is less effective when coming forward.
Magilton's return has given the Blues more cohesion in midfield, while Kevin Horlock continues to look a valuable addition sitting in front of the back four and putting a boot in when required.
Up front, Kuqi took his goals well, while Bent — who gave little indication that he was immediately on his way out of Portman Road — was a constant threat.
Town: Davis, Diallo, Wilnis, De Vos, Naylor, Magilton (Dinning 76), Miller, Horlock, Westlake, Bent (Bowditch 69), Kuqi.