Veteran striker Dion Dublin produced a stunning goal as pre-season promotion favourites Leicester snatched their second win of the campaign.
The 35-year-old ex-England frontman lashed an unstoppable 25-yard volley on the hour to settle jittery City.
It came as rock-bottom Rotherham looked for a way back after being caught out with Leicester's opener two minutes before half-time.
French midfielder Lilian Nalis gave the Foxes the lead with his side's first serious attempt on goal.
It was a gem of a strike from the 32-year-old that caught out Rotherham after the Yorkshire side had the edge in the first half. Kevin Harper whipped in a curling cross from the right and Nalis darted in to volley past Mike Pollitt from 12 yards.
It was tough on the home side who had created a string of chances.
Micky Adams' reshaped side were second best as Rotherham carved out opportunities thanks to winger Chris Sedgwick and midfielder John Mullin.
Sedgwick picked out Mullin with an early cross, but the resulting volley was driven just over and another Sedgwick cross was headed away by Dublin, helping out at the back.
Richie Barker met another Sedgwick cross, but looped his header over and Mullin stretched to poke a Sedgwick ball into the area but former Sheffield Wednesday keeper Kevin Pressman, making his City debut, held on to the chance.
Rotherham's appeals for a penalty were then dismissed after Paul Shaw crashed down in the area under a challenge from Nikos Dabizas.
When Leicester claimed the lead it was the fourth match in a row Rotherham had conceded just before half-time.
Only a last ditch clearance by ex Arsenal defender Martin Keown kept Rotherham out early in the second half and Pressman had to bundle the ball away as Barker came close to prodding the ball over the keeper.