The Millers are just a point off second place after Bournemouth were thrashed 5-0 at Morecambe, and a double strike from Kevin Ellison set them on their way.
In a pulsating game from start to finish, it was Bradford who took a 19th minute lead after early Rotherham dominance.
Nicky Law, returning to his old club, saw a fierce shot tipped away by Eastwood and Ian Sharps then headed over from 10 yards, as Drewe Broughton received an early yellow card.
But Lee Bullock broke the deadlock for the Bantams as he stabbed home past Andy Warrington after Simon Whaley's free kick had spun off the end of the defensive wall and fell kindly for the frontman.
The Millers responded once again with an Adam Le Fondre effort, but the league's top scorer was to have a relatively quiet afternoon.
Michael Boulding was forced off with injury just a minute later, and Ellison levelled on the half hour, slamming home the rebound after Eastwood had brilliantly blocked Broughton's goalbound effort following good work from Le Fondre on the right.
Just seven minutes later the fired up Ellison shot Rotherham infront as he burst into the box from the left having swapped wings with Adam Rundle and drove a crisp shot low past Eastwood.
Bradford almost hit back before the break but after Simon Ramsden set up Whaley his shot flew wide.
The Millers shot themselves in the foot a few seconds after the break as straight from the kick off, Michael Flynn pounced on a stray ball in the area and lashed the ball past Warrington.
The Millers new look back line then had to withstand a severe ten minutes of pressure before Danny Harrison was brought on, with Law moving wide right.
Almost immediately the game settled to it's most unfrantic period. Sharps missed the Millers best chance to extend their lead as he somehow hit the post from a few yards as City's zonal offside trap failed from Law's free kick.
And Bullock then almost gave City the lead as his first time shot was superbly tipped over by Warrington from 15 yards, and the Millers stopper tipped another effort over a short time later.
Gary Roberts then took centre stage with probably one of the goals of the season, as his quick thinking and perfect execution gave the Millers the lead again with 12 minutes left.
The midfield man fired in a dipping effort from all of 45 yards from a very quickly taken direct free quick on the far touchline that left Eastwood embarassed and nestled in the net.
Warrington then tipped O'Brien's effort over the bar with just five minutes left to cap a super display of goalkeeping.
And as City pressed for the equaliser in the final ten minutes, Broughton tapped in Le Fondre's ball across the goalline as he beat the offside trap despite home protests to bag the points on a thrilling afternoon.