Promotion-chasing Rotherham made it two wins in a week with an important victory over their local rivals Chesterfield at the New York Stadium.
Jonny Mullins scored the only goal in the 57th minute with a header from David Noble’s corner.
Steve Evans’s side dominated the first half with striker Daniel Nardiello hitting the post before drawing an excellent save from Tommy Lee.
Armand Gnanduillet could have equalised late on but he miscued his header.
Rotherham climbed to sixth with the win and are now just one point behind third-placed Burton Albion with two games in hand.
Rotherham: Warrington, Bradley, Mullins, Davis, Ridehalgh, Noble, Arnason, Frecklington, Kearns, Revell, Nardiello. Subs: Thompson, Tonge, Slew, Pringle, Odejayi, Agard, Cameron.
Chesterfield: Lee, Talbot, Trotman, Cooper, Smith, Whitaker, Hird, Togwell, O’Shea, Richards, Lester. Subs: Barrington, Clay, Brindley, Gnanduillet, Wafula, Randall, Townsend.
Referee: Paul Tierney (Lancashire)