The Millers, who were favourites heading into the game against the newly promoted Dons, were left stunned as Karl Robinson's side romped to a 4-1 victory at the New York Stadium, recording Rotherham's worst opening day result in 21 years.
A number of Rotherham players found themselves under the microscope after the game. However, none more so than Derby loanee Roos.
The 23-year-old had been impressive in pre-season, but failed emphatically to recapture the same form as he ended up picking the ball up from out of his own net on four separate occasions on his Championship debut.
The clearly frustrated Millers fans vented their anger over Twitter at the young keeper's performance, with one naming him the worst keeper to ever grace a football pitch.
Not seen a goalkeeping display like this since the Cutler/Montgomery days. Feel for Roos. #rufc— Gareth Simmons (@GarethSimmons) August 8, 2015
What on earth is Kelle Roos doing? Cost us 3 goals in 45 minutes... #rufc— Deeeaaanooo (@deano94rufc) August 8, 2015
Although, it wasn't all demoralising comments for the Derby goalkeeper, with one fan calling for the fans to get behind him for the next match:
Glad to see lot of #rufc fans slagging Roos off after 1 game, that's really going to help him!! Get behind the young lad.— joe hadfield (@twinj1) August 10, 2015
On his Football League debut, it was always going to be a nervous occasion for the Dutch stopper and the occasion seemed to get the better of him.
The comments towards Roos, while clearly in frustration, will only work against the youngster building his confidence and coming back better in the next match. If anything, it will have just put more pressure on the shoulders of a young keeper who is clearly in need of a confidence boost.
Steve Evans will have to work extremely hard to get Roos confident again, especially with some of the fans working against him, otherwise it could be a loan spell that turns out badly if frustrations builds, but ultimately it is up to the goalkeeper himself to make it work.