Arnason's starring role
Arnason had a hand in all three goals, opening the scoring after 25 minutes with a spectacular effort from outside the area which flew in the top corner.
Ten minutes later The Millers doubled their lead, Arnason delaying his pass before finding the run of Nardiello who slotted the ball, left footed, past home goalkepper Andy Marriott.
Advertisement
Hide AdAdvertisement
Hide AdMansfield Town came out on the attack after the break and soon pulled a goal back, Lee Stevenson scoring a rocket of a shot from the edge of the area which left substitute goalkeeper Scott Shearer with no chance.
The Millers two goal advantage was restored on 70 minutes, Arnason's long throw was flicked on by Mullins to the unmarked Mark Bradley who calmly fired home.
The home team did find another goal, Matt Green shooting through the legs of Scott Shearer to give Mansfield a glimmer of hope heading in to the final stages.
However it was Rotherham United who finished the game stronger after Alex Revell laid back to Gareth Evans who rattled the crossbar with a curling effort.