In difficult conditions, with heavy rain and thunder in the latter stages, Rotherham survived an early scare as Scott Wiseman cleared a header from a Gretna corner off the line.
In almost Rotherham's first attack though they took the lead on five minutes as Delroy Facey provided the flick on for Hoskins to run through and provide a tidy finish. Trialists Eugen Bopp and Alexis Nicolas made an appearance from the kick-off and looked impressive on the ball, Bopp having two shots skimming wide of the mark. Then Facey missed when it looked easier to score from only a few yards as he put Wiseman's inviting cross wide to the amazement of the Millmoor crowd.
The second half resumed with the Millers taking control as Hoskins added a second, neatly sliding the ball past Main into the bottom corner as the stopper tried to spread himself. Monty replaced 'keeper Cutler after 53 minues as Nicolas and Partridge had efforts saved at the other end after the latter combined well with Wiseman, before the visitors pulled a goal back.
However their joy was shortlived when soon after Ryan Taylor sprung on a loose back pass to slide the ball under the keeper's body and make it four pre-season goals after his hat-trick at Grantham last Saturday.
The game also saw trialist Rhys Powell get an outing and midfielder Lee Williamson play the last 20 minutes as he recovers from a shoulder operation and a bug he picked up late in the week.
Millers team: Cutler (Montgomery 53), Wiseman (Pritchard 78), Robertson (McMahon 78), Nicolas (Williamson 68), Sharps (Worrell 73), Mills (Powell 78),
Partridge (Duncum 60), Bopp (King 78), Hoskins, Facey (Taylor 63), Keane (Brogan 73).