Lancashire overcame a nervous period in the second half to prevail in this opening match of the County Championship at Fylde RFC
Lancashire led by 22-5 at half-time and looked comfortably placed, but Northumberland rallied strongly and at 27-26 it became a tough call for the Red Rose.
But they overcame that sticky period to prevail in the end as they finished with a flourish, ending all arguments with three late touchdowns.
Northumberland went ahead after seven minutes with a try by fly-half Will Muir.
Evan Stewart tied up the scores at 5-5 with a pushover try,
Lancashire assumed the lead on 20 minutes as try-scorer Mark Goodman (Sedgley Park) latched on to a neatly-slipped pass by Fylde centre Connor Wilkinson.
The pushover ploy worked again for Lancashire after 37 minutes as the home pack shoved their counterparts backwards in relentless style before Rossendale lock Reece Tomlinson got the final touch to claim the try.
In the ninth minute of added-on time, Fylde's Matt Lamprey scored Lancshire's fourth try, yet again from a pushover.. Team-mate Greg Smith added the conversion as Lancashire led 22-5.
Northumberland started the second half with attacking intent and within two minutes of the kick-off crossed the Lancashire line with a try from second row Michael Walton, goaled by Muir.
Lancashire quickly got on track with an opportunist try by Wilkinson
Northumberland wing Aedan Maloney dashed in for a long-range interception try, augmented by Muir to reduced the gap to eight points at 27-19.
A careless pass by Armstrong near his own line proved costly and it went straight into the arms of Tom Grimes, who had an easy task to score, Muir converting in front of the posts to make the score 27-26.
Armstrong made up for his error on 70 minutes with a splendid solo try from deep, crashing his way through an attempt at a tackle as he finished off his 65-yard run with aplomb. Smith added the goal points to ease the home side's nerves.
Evan Stewart sped over for a late try after a clever pass from Smith, who added the goal points.
Then to round it off, Armstrong claimed another try after excellent work by Preston's Niall Crossley.
Earlier, Lancashire women scored a 51-10 win over Northumberland at the Ansdell ground to maintain their 100 per cent record in the competition.