Two Ricky German strikes and another from Joe Rowley saw the Spireites reserves cruise to a comfotable 3-0 reserve-team victory at the Proact.After a German burst ended with a shot being fired wide, Rowley headed home from inside the box to give the hosts the lead, the youth team player owing a debt to returing right-back Liam O'Neil and his pinpoint cross.
Trialist Shaun Okojie created a chance when he anticpated a through ball and bore down on goal, though his low shot was saved by United 'keeper Harry Fiddler's legs.
Before the interval the lead was doubled when German showed his strength to battle round his man in the box before desplaying a cool head to slot home a low finish.
The Spireites started the second half as they finished the first, German forced a good save at the near post before, on 50 minutes, Okojie headed an inswinging corner wide when he could have done better.
Home chances were coming and going, Rai Simons swung at a volley that flew well over the bar while Rotherham's best chance of the game to that point fell to Kai Herbert at the back post, but the subsitute couldn't convert from close range.
German netted his second with just over ten minutes remaining as he latched onto Jack Brownell's low centre to convert via the far post to complete the scoring.
Chesterfield: Allinson (gk), Daly, Brewitt, Smith (triallist 11'), O'Neil (c) (Brownell 46'), Rowley, Dimaio, Simons, Beesley, Okojie, German
Subs not used: Jones (gk), Hand
Fiddler (gk), Southern-Cooper, Warren, Murr (Herbert 54'), Bailey, Rose, Kayode (Martin 54'), McGinley (Abraham 46'), Yates (c), Carlton (Coleman 69'), James (Parnell-Wilson 59')
Chesterfield: Rowley 17', German 42' 77'