F-T: Northampton Town 0 Rotherham United 3
Rampant Rotherham United turned on the style as their League One promotion push gathered new momentum at Northampton Town.
The Millers dominated from start to finish and won at a canter to put back-to-back defeats behind them and consolidate their place in fourth spot.
Manager Paul Warne made five changes from the midweek loss at MK Dons and his bravery paid off with one of the best performances of the season.
Michael Smith put Rotherham in front before the break and second-half goals from David Ball and Richie Towell completed a victory which could have been even more comprehensive.
Smith scored the opener in the 17th minute, controlling Will Vaulks' long ball perfectly before beating former Millers goalkeeper Richard O'Donnell with a low shot.
O'Donnell pulled off a wonder-save to deny Towell four minutes later and was called into action again to keep out a David Ball effort after the Millers striker had made space for himself in the penalty area.
There were several other near-misses as Paul Warne's men attacked the end housing more than 1,000 travelling Rotherham fans.
Rotherham were so much in control that it took the home side 56 minutes to muster an attempt on target, Hildeberto Pereira's shot bringing ironic cheers as Marek Rodak saved.
Jon Taylor robbed the Cobblers defence soon after and was foiled by O'Donnell, but the visitors were 2-0 up just past the hour mark when Ball latched on to Ryan Williams' cross and his shot had too much power for the Northampton keeper.
Towell added an exquisite third with nine minutes, his sublime finish matching the build-up work of Smith and Williams.
Rodak had to save a Matt Grimes free-kick in time added on but the contest had long been over by then.
Northampton (4-2-3-1): O'Donnell; Moloney, Taylor, Turnbull, Bunney; O'Toole (Van Veen 70), Grimes; Hoskins (Ariyibi 58), Pereira, Powell; Luckassen (Mathis,79). Subs: Cornell, Barnett, McWilliams, Facey.
Rotherham (4-4-2): Rodak; Emmanuel, Ajayi, Vaulks, Mattock (Ihiekwe 67); Taylor (Forde 67), Towell, Palmer, Williams; Smith, Ball (Newell 84). Subs not used: Price, Wood, Lavery, Yates.
Goals: Smith 17, Ball 61, Towell 81 (Rotherham).
Referee: Ben Toner (Lancashire).
Attendance: 5,882 (1,129).