Alnwick started well and took an early 3-0 lead with a penalty from Evan Moir, but the visitors hit back and within 30 minutes they had their noses in front at 3-12.
However, the home side were then awarded a penalty try which got them back in contention at 10-12 and that was how the scoreline remained to half-time.
Alnwick made a great start to the second half and a try in the corner saw them retake the lead at 15-12 , but Jake Woods was then sin-binned for ten minutes, and during his absence, Blackburn took full advantage to run in a try of their own, which was converted, to put them back in front at 15-19.
Alnwick tried to force their way back into the game, but they were thwarted when a long range penalty after 73 minutes saw the visitors extend their lead to 15-22.
Another converted try in the closing stages finally took the match out of the Northumbrians’ reach.
The defeat leaves Alnwick in sixth place on 39 points from their 13 games played, having two games in hand on the team immediately above them in the table.
On Saturday (January 15), Alnwick face another difficult game when they are away to Lymm, who are just three points behind them in the standings on 36 points.