Victory at the New York Stadium would have sent Derby back to the summit but they were heading for defeat until loan signings Ince and Darren Bent rescued a point.
Paul Green put Rotherham in front against his former club but the home side had barely finished celebrating when Ince equalised with a sublime finish.
Two goals in the space of five minutes from Richie Smallwood and Matt Derbyshire put Steve Evans' side in command early in the second half, but Derby were not finished yet.
Ince's fifth goal in three games since his loan move from Hull City gave the visitors hope and Bent took his tally to six goals in seven appearances seven minutes from time to send Derby above Middlesbrough on goal difference into second place.
Jason Pearce's debut goal gave beleaguered Wigan Athletic their first victory since Boxing Day as Reading were beaten 1-0 at the Madejski Stadium.
Rudy Gestede's late strike ensured Blackburn Rovers drew 1-1 at his former club Cardiff City in the other Championship game on Tuesday.
MK Dons won 1-0 at Colchester United to move up to second spot, while fifth-placed Sheffield United were 2-1 winners at Notts County.
Doncaster Rovers moved into the top six by beating Crewe Alexandra by the same score, while Chesterfield dropped down to eighth after losing 2-0 at Scunthorpe United.
Luton Town missed an opportunity to move up to third place when they were beaten 1-0 at Mansfield Town in the only League Two game of the day.
