Boro were 1-0 up inside the first ten minutes when Juninho corled a 20 yard free-kick into the top corner after Szilard Nemeth was brought down.
Boro did not have it all there own way as the Division 1 side showed why they were once play-off hopefuls last season.
Boro took a 2-0 goal advantage early in the second half but not before the Millers had hit the post, after sloppy work by Doriva. Malcolm Christie finished good work by Gareth Southgate and Juninho.
The home side fought back with a goal from Alan lee after an hour but Doriva restored Boro's two gaol cushion five minutes later.
Boro dominated the final quarter and could have made the scoreline more comfortable but will settle for the excellent workout. Five players including the Brazilians Juninho and Doriva will benefit from a full 90 minutes of action.
Boro team:
Schwarzer (Crossley 65)
Parnaby (Stockdale 86)
Wright (Cooper 80)
Doriva
Riggott
Southgate (Davies 82)
Wilson (Marinelli 53)
Nemeth
Christie (Downing 53)
Juninho
Greening