Two goals in as many second-half minutes from James Hayter and David Healy spoilt any hopes Kenny Jackett had of marking his third anniversary in charge of Millwall with a win as The Lions slipped to a second successive away defeat at the Keepmoat Stadium.
Having been in control for much of the opening half and established a 12th-minute lead courtesy of Steve Morison's eighth goal of the season, Jackett's men contrived to throw away their hard work cheaply with Hayter (55mins) and Healy (57mins) turning the tables in Rovers favour.
The Lions boss was barely able to hide his frustration as he said: "We went 1-0 up and had a couple of chances to extend the lead.
But Doncaster had a 10-minute spell at the beginning of the second half where they dominated and ultimately won the game.
I was pleased with how we responded and had chances, but didn't take them."
A spate of niggling injuries left The Lions unable to call on the services of Neil Harris, Chris Hackett, Tamika Mkandawire and Theo Robinson.
In came Darren Carter and Kevin Lisbie for Danny Schofield and Robinson, with boss Jackett pushing Liam Trotter further forward to play just behind Morison in a 4-4-1-1 formation and Lisbie starting wide on the left flank.
On a heavily watered pitch that saw a number of players lose their footing in the opening half, it took seven minutes for Millwall to register the first really constructive attacking move of the game.
Morison slipped a finely weighted pass down the line to James Henry, but with Trotter powering forward into the six-yard box, the winger's floated cross was too close to keeper Neil Sullivan, who gratefully gathered.
However Sullivan's handling was not so assured five minutes later. On this occasion Henry scampered down the right before hanging a deep cross for the unmarked Trotter at the far post. Although Sullivan appeared to have Trotter's header covered, he allowed the ball to squirm out of his hands and with it trickling slowly towards the goal-line, Morison made sure and applied the finishing touch.
Henry hit a first-time effort wide with the outside of his right boot before debutant Healy, signed by Rovers from Sunderland this week, hit a crisp shot that was comfortably dealt with by David Forde in the visiting goal.
Forde then acted swiftly to avert the danger, blocking James Coppinger's angled drive with his feet as Donny began to ask questions of the Millwall rearguard.
But it was The Lions who could have doubled their tally 10 minutes before half-time; Morison's sliderule pass picked out Trotter, who powered forward before firing a shot that looked destined for the bottom right hand corner until keeper Sullivan atoned for his earlier error to fling himself low and get the feintest of touches to push the ball away for a corner.
Rovers looked - and proved to be - a totally different proposition after the break with a much improved performance.
Most perplexing for The Lions, however, was that the structure and cohesion which had served them so well in the opening 45 minutes disappeared in a torrid opening spell to the half that ultimately proved decisive.
Millwall had already had a let-off on 50 minutes when a bursting run by Coppinger was halted by Scott Barron, who earned a yellow card for his foul. Brian Stock's free-kick was met by Shelton Martis, and his powerful header flew narrowly over the bar.
But there was to be no let-off five minutes later when Morison was penalised for a foul, Joseph Mills swung in a free-kick and Hayter was on hand to nod past Forde from close range.
The celebrations had barely died down when Northern Ireland international Healy made it two, capitalising on a loose ball to guide home with Forde stranded, although Alan Dunne looked to be fouled in the build-up.
It could have been even worse for the beleaguered Lions when Coppinger's outrageous piece of footwork on the right set up Healy; the latter's shot had the power but not the curl and flew wide.
With Millwall looking edgy and uncomfortable in possession, Jackett introduced Schofield for Carter and within three minutes The Lions should have been handed an opportunity to draw level. However when Morison wriggled an opening on the left and whipped over a delightful cross, any hope Lisbie had on connecting with the ball was thwarted by the attentions of home defender Wayne Thomas, whose vice-like grip virtually wrestled him to the ground.
Another game, another non-penalty for Millwall...
On came teenage striker John Marquis, who came agonisingly close to scoring his first ever senior goal for the club, spinning on a sixpence and firing a low shot that flashed a whisker wide.
Schofield's effort was then blocked before Marquis, again, was left holding his head in despair, this time after heading straight into Sullivan's hands from no more than six yards.
Doncaster should have been reduced to 10 men three minutes from time when Thomas somehow escaped with just a yellow card following a forearm smash that thankfully didn't connect properly with Lisbie's face.
Barron's subsequent free-kick was met by Marquis, but the youngster couldn't direct his header on target.
A generous four additional minutes of injury time saw Donny run down the clock comfortably to leave The Lions smack bang in midtable, five points off the Play-Offs and as many away from the drop zone.
Doncaster Rovers: Sullivan, Mills, Thomas, O'Connor, Martis, Hayter, Oster, Stock, Shiels (Wilson, 86mins), Coppinger (Dumbuya, 90+3mins), Healy (Brooker, 86mins). Subs not used: Webster, Hird, Woods.
Booking: Thomas (87mins)
Scorers: Hayter (55mins), Healy (57mins)
Millwall: Forde, Dunne, Barron, Abdou, Robinson, Shittu, Carter (Schofield, 64mins), Trotter, Lisbie, Morison, Henry (Marquis, 71mins). Subs not used: Mildenhall, Craig, Ward, Laird, Hughes-Mason.
Bookings: Barron (50mins), Morison (55mins)
Scorer: Morison (12mins)
Ref: S. Mathieson
Att: 10,356 (away 684)