Millwall cling on to secure a very useful three points in South Wales and ensure they are right in the fight for the play-offs in an incredible tight table.
Tom Bradshaw netted the only goal in the first half and could have had another were it not for city keeper Ryan Allsop.
As for the Bluebirds it's another defeat and now nine games without a win in the Championship dating back to November, they remain fourth-bottom.
Blackburn's bid to go an entire season without drawing a match comes to an end at the 28th attempt.