Robins had been recalled from a loan spell at Bristol City, where he had bagged five goals in eight games, after Millers boss Ronnie Moore lost patience with his out-of-form strikers.
And he responded with a superb display, including netting Rotherham's opener after 20 minutes as the Millers notched their first win in seven games.
It came when Chris Sedgwick had a shot deflected and Robins jumped to beat keeper Kelvin Davis to head home from four yards.
After that he could have had another, but was inches away from connecting with a Sedgwick cross and in the dying minutes of the first half had the ball whipped off his toe on the goal-line by defender Ben Chorley after great work by Gareth Farrelly and Richie Barker.
Rotherham bossed the first half, with Wimbledon's best effort being a David Connolly free kick which was palmed out for a corner by Mike Pollitt, and it was just reward when the home side notched a second three minutes after the break.
Sedgwick sent John Mullin haring down the right and his delightful cross was headed home by big defender Guy Branston, with the Dons' defence flat-footed.
But after that Wimbledon came back into it as the Londoners were desperate to take home some reward in their pursuit of a play-off place.
They grabbed one goal back after 58 minutes when David Connolly found space in the box to tuck a Wayne Gray cross past Pollitt from 16 yards - but they found further chances few and far between.
Rotherham could have wrapped it up when Robins opened the door with a classy cross-field ball to Sedgwick, but his shot was saved by Davis and in the dying minutes Alan Lee looped a header over the bar.
Millers boss Moore said afterwards: "We let Mark go to Bristol to get some games under his belt and it certainly paid off. He's a quality striker and will always get you goals."
Robins, though, would not mind if a move back to Ashton Gate is allowed, with one eye on Bristol City's forthcoming LDV Trophy Final looming against Carlisle next month.