Jon Stead marked a dream debut for Blackburn with the only goal.
Middlesbrough had the better chances in the first half but failed to capitalise as Gaizka Mendieta wasted two of their best opportunities.
Stead gave Rovers a half-time lead with a low right-foot shot after the ball fell kindly to him following Danny Mills' tackle on Paul Gallagher.
Juninho forced a superb save from Brad Friedel after the interval, but Boro again failed to take their chances.
Blackburn went into the match without a win in five games - and boss Graeme Souness responded by dropping strikers Andy Cole and Dwight Yorke, handing a debut to new signing Stead alongside fellow youngster Gallagher up front.
But it was Boro who threatened first, when Massimo Maccarone's ball over the top set up Mendieta, who shot wide of Friedel's goal in only the third minute.
Chances were rare, with Doriva and Boudewijn Zenden both failing to trouble Friedel from distance, before Mendieta curled a tame shot into the American's hands.
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KEY MOMENTS
3 mins: Gaizka Mendieta fires wide for Boro
39 mins: Jon Stead scores on his Blackburn debut
63 mins: Rovers keeper Brad Friedel saves well from Juninho
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At the other end, it took Blackburn 36 minutes to have a shot - and Andy Todd's effort swerved so wide that it went out for a throw-in.
However, Stead soon opened his Rovers account, as Gallagher's run was halted by Mills' tackle, but the ball fell perfectly for the former Huddersfield man to score from eight yards.
Stead went close twice more before half-time - and Boro boss Steve McClaren hauled off Maccarone and Stuart Parnaby at the interval, to be replaced by Joseph-Desire Job and Stewart Downing.
Cameroon international Job was soon involved in the action, setting up Juninho, who fired over the bar.
But McClaren's men continued to miss chances, although Rovers were indebted to Friedel for an impressive reaction save from Juninho after the Brazilian had been set up by Mendieta.
Stead, looking for his second, then could only manage a weak shot rather than passing to substitute Matt Jansen, who had looked better-placed.
Defender Gareth Southgate nearly levelled in the dying minutes, but Craig Short cleared off the line.
Friedel then saved well from Zenden as the Rovers defence held firm for their first win since 28 December.
Middlesbrough: Schwarzer, Mills, Southgate, Riggott, Queudrue, Mendieta (Nemeth 66), Parnaby (Downing 45), Doriva, Zenden, Juninho Paulista, Maccarone (Job 45).
Subs Not Used: Jones, Cooper.
Blackburn: Friedel, Babbel, Todd, Short, Gray, Emerton, Douglas, Flitcroft, Neill, Stead (Tugay 85),
Gallagher (Jansen 65).
Subs Not Used: Enckelman, Cole, Johansson.
Booked: Douglas.
Attendance: 28,307.
Referee: R Styles (Hampshire).