Adam Lockwood and James Hayter were on target in the opening 17 minutes for Rovers as the Bluebirds were knocked off their perch as the early-season pacesetters, with West Brom leapfrogging them at the top of the table.
Lockwood headed in from six yards and Hayter struck a right-footed shot beyond helpless Cardiff goalkeeper David Marshall from inside the box as Sean O'Driscoll's men recovered from their 5-1 Carling Cup capitulation to Tottenham.
Peter Whittingham extended Doncaster goalkeeper Neil Sullivan from 25 yards midway through the second half, but it was the closest Cardiff came as Dave Jones' side struggled to build on their early-season form.
Michael Chopra and Chris Burke were both guilty of missed chances as Doncaster claimed a first league win of the season.
Cardiff were top of the standings following three wins and a draw in the opening month of the campaign, but they were always chasing in South Yorkshire.
The return from injury of Jay Bothroyd, one of four changes to the Cardiff team from the midweek Carling Cup win over Bristol Rovers, was short-lived as the striker was replaced by Kelvin Etuhu after nine minutes.
And Cardiff's woes were compounded three minutes later when Rovers scored the opener.
Martin Woods' corner to the near post was met by Lockwood, who powered in his second of the season.
A shell-shocked Cardiff conceded a second when, four minutes later, Hayter moved into the left side of the penalty area and arrowed a shot into the top-left corner.
Marshall had conceded two goals in the opening four league fixtures having watched his colleagues net 11 at the other end.
But now the Scotland stopper, who has conceded 11 goals in three international starts, was facing another large reversal.
Meanwhile, former Scotland goalkeeper Sullivan was largely a spectator at the other end.
The ex-Wimbledon and Tottenham stopper was first called into action nine minutes from the interval when he saved Burke's tame effort.
Marshall prevented Doncaster extending their advantage seven minutes after the interval, turning Woods' 18-yard shot round the post.
Burke then dragged a shot wide and Chopra's right-footed effort from the edge of the box was caught by Sullivan.
Sullivan was at full stretch to deny Whittingham's left-footed shot from 25 yards as Cardiff tried to break through the Rovers rearguard.
Chopra then failed to test Sullivan once again as Cardiff continued to toil in front of goal.
Doncaster continued to search for a third on the break and Marshall was forced to tip over Woods' effort from the right as Rovers claimed a welcome win.