Rovers had been warned: this game has a habit of biting you on the backside.
And Paul Dickov’s pre-match musings could not have been more apt as Federico Macheda read the script that Rovers’ boss must have been fearing all week.
It was Sod’s law that Macheda - cast to one side by Doncaster to pave the way for Billy Sharp’s homecoming - should take centre stage, up-staging James Coppinger on his landmark 400th appearance to leave both his current and former loan clubs still teetering on the brink of Championship survival.
Rovers could consider their bums well and truly bitten as the Manchester United striker took his tally to nine goals in 12 appearances for the Blues. He was ditched by Doncaster after scoring three in 15.
Especially sore will be the behind belonging to James Husband, after the young defender’s lapse in concentration allowed Macheda to pick his pocket and cancel out Paul Quinn’s first half finish, the spark for what had earlier seemed a very unlikely City comeback.
Doncaster were the architects of their own downfall.
Roused by supporters’ raucous minute’s applause for Coppinger in the 26th minute, Rovers grabbed a timid game by the scruff of the neck when Quinn slammed home.
Before the game Coppinger had been presented with a plaque by Rovers’ all-time record appearance maker Colin Douglas.
But in the second half it was Doncaster’s players who were handing out gifts left, right and centre as Macheda helped himself to a brace, either side of another X-rated defensive lapse which allowed Lee Novak to prod the visitors ahead.
Birmingham’s comeback - and the nature of Rovers’ collapse - was head scratchingly bewildering.
Lee Clark’s men, with the exception of lively winger Chris Burke, looked every inch a side low on confidence and belief before the break.
So when Doncaster struck the first blow through Quinn, the defender lashing home after Chris Brown nodded David Cotterill’s free kick back across goal, there was an air of confidence around the Keepmoat.
After all, Rovers had not lost at home in the league since Boxing Day and when they scored the first goal in four out seven games during March, they went onto win every single one of them.
Those stats prompted Brown to quite rightly point out last week that scoring the first goal settled Rovers and was key to their upturn in form. The opposition scoring first, he said, had just the opposite effect; panic tended to set in.
Rovers, patient in their approach play, had done the first part of their job in no thrills fashion. They had once again assumed the lead and appeared to be in a position of relative control as the game headed towards the hour mark.
Then they pushed the self destruct button. Husband, with plenty time to clear, allowed Macheda to steal it off him and level - and in an instant the game turned on its head.
Visibly stunned by the setback, Doncaster retreated into their shells and the panic that Brown talked about during the week had well and truly set in.
Birmingham all of a sudden had their tails up and they soon had the lead, courtesy of more poor Rovers defending. Goalkeeper Darren Randolph’s clearance caught the hosts’ backline flat footed and sent Novak clear to prod past Johnstone, despite Quinn’s best attempts to keep it out.
And with Rovers on the ropes it was quickly 3-1 and game over, when Tom Thorpe headed Paul Robinson’s free kick back across the face and that man Macheda was in the right place again to nod home.
On reflection Dickov’s side had missed the experience of wily campaigners Richie Wellens and Abdoulaye Meite - the latter pulling out during the warm up and forcing Coppinger to play at right back on his special day - which might have helped them see the game out.
But the cold, hard truth of the matter was that Rovers had gifted their opponents all three points on a day when victory - and the extra breathing space at the bottom it would have afforded - was there for the taking.
That it was Macheda who did the damage was a typical quirk of fate in sync with a rollercoaster season.
The finish line is in sight for Doncaster but this was a rather clumsy stumble that could have been avoided. It’s left Rovers nursing a rather sore behind - but they have to quickly pick themselves up and dust themselves down for the visit of Bolton tomorrow night.
Once bitten perhaps, but Rovers cannot afford to be twice shy on a big night against the Trotters.