Armstrong - now starting his third season with the club - fired home his first goal in Stamford colours to spark a second half spree to seal success in the Pete Down Memorial Cup clash with their United Counties League Division One hosts.
After conceding 11 goals in their opening pre-season clashes with higher level Peterborough United and King's Lynn, Daniels manager Graham Drury had urged his side to assert their authority over the step six Arrows.
Drury commented: "We did a professional job like King's Lynn did to us. It was nice to start scoring goals and to keep a clean sheet as well.
"It was important we did things right. We kept our consistency throughout despite making changes and playing some different shapes.
"It kept the purpose of the three games. It identified a few things and also showed a few flaws as well as some positives."
The Daniels dominated the opening exchanges but, despite raining in several shots on the home goal, were unable to find the vital breakthrough.
Liam Adams lifted a couple of speculative shots wide while the lively Cosmos Mathwasa also went close with another effort.
Home goalkeeper Yinka Abebowale then produced a string of fine saves to keep the Daniels at bay as they cranked up the pressure in the build-up to half-time.
Mathwasa was twice thwarted by brave saves from Abebowale after his electic pace had created openings while Armstrong saw a sweet strike tipped to safety by the Arrows custodian.
Despite making several changes at the break, Stamford continued on the offensive with Mathwasa a regular raider on the home goal.
He was again denied by a smart stop from Abebowale from close range before being involved in the move that finally broke the deadlock after 57 minutes.
James Hicks, James Siddons and Mathwasa all linked up well to tee up Armstrong who curled home his maiden Daniels goal into the bottom corner.
The Daniels then doubled their lead five minutes later as Siddons' flick on released strike partner Hicks who coolly slotted home past the advancing Abebowale.
A third Stamford goal then followed after 68 minutes when Dec O'Hare was clipped in the box by Leigh Warman and Hicks stepped up to confidently convert the resultant spot kick.
Stamford's superior fitness then started to shine through in the latter stages as they added a fourth goal with 15 minutes remaining against a Harrowby side who had beaten Northern Premier Division neighbours Grantham Town in a penalty shoot-out in the inaugural South Kesteven Charity Cup semi-final at the weekend.
Mathwasa was again instrumental in the build-up which saw Hicks' shot parried by Abebowale for O'Hare to pounce and finish with aplomb for his second successive Stamford strike.
The scoring was wrapped up in the dying throes as a slide-rule pass from Olly Brown-Hill released Harry Vince whose low cross was converted by Siddons for Stamford's fifth and final goal.
The match was played in memory of former Stamford player and Harrowby manager Pete Down.
Down was part of the Stamford side which reached the final of the FA Vase in 1975/76 before losing to Billericay.
His son Chris - who presented the trophy to Stamford skipper Dan Haystead - said the Vase final was the 'best and worst day' of his dad's life as he 'hated losing.'