Boro started the game well and were ahead as early as the sixth minute. Hayden Coulson was the architect and Sammy Silvera profited with an excellent finish for his first goal in Boro colours.
Morgan Rogers almost followed that within two minutes. First he was denied by Viktor Johansson, then we he did beat the Rotherham goalkeeper 30 seconds later, he was denied by an offside flag.
Rogers was denied again by Johansson after good work by Hayden Hackney as Boro continued to dominate the contest.
Both Silvera and Rogers went close to furthering the advantage shortly before the half-time whistle brought an end to Boro’s best 45 minutes of the summer.
The interval brought a complete change of XI for Boro and including a return from illness for Matt Crooks, who was denied an early goal when his goal-bound chip was cleared by Tyler Blackett.
Once again, Boro were the better side and with 20 minutes left on the clock Alex Gilbert was introduced for his first appearance on UK soil. Rotherham made further wholesale changes for the closing stages.
Riley McGree and Gilbert almost combined to score a second goal, but stalwart defender Sean Morrison cleared the danger for the Millers.
The second goal did come, though, with four minutes remaining, and it was Gilbert who rounded off some good play with a smooth finish into the bottom corner.
Boro (1st half): Dieng, Smith, Barlaser, van den Berg, Hackney, Jones, Payero, Silvera, Rogers, Coulson, Lenihan.
Boro (2nd half): Glover, Collins, Fry, McGree, Sykes, Stott, Hoppe, Agyemang, Hannah, Forss, Crooks (Gilbert 70)
Subs: Bilongo, Jones.
Att: 2017 (489 Boro)
