Armstrong duly departed, wincing at the pain of a sprung rib cartilage he suffered in his line of duty as the bravest of scrum-half bravehearts. The painful fact for Scottish rugby is that the natural heirs to the Laidlaw and Rutherford dynasty have, in the past three years and eight months, spent just 74 minutes together on the international stage.
Their most recent acquaintance before Saturday was the Calcutta Cup match at Twickenham on 6 March, 1993. Chalmers was the wounded partner that afternoon, withdrawing from the heat of battle with a broken arm. Now injury time has arrived again and one of the questions begged by Scotland's patchy performance against Australia is whether the ageing double act - Armstrong is 30, Chalmers 28 - will be granted another chance on the big stage.
The unlikely duo - Armstrong with his tousled hair, his rugged face and his appropriately scavenging-like play; Chalmers with his coiffured mane, his cherub cheeks and almost languid stand-off style - first appeared at Murrayfield together as try-scorers in the defeat of Wales in January 1989. Seven years and 10 months later, they are still eight matches short of the record 35 internationals Roy Laidlaw, Armstrong's mentor at Jed- Forest, and John Rutherford played in tandem as Scotland half-backs.
The clamour grew in the aftermath of Saturday's defeat for the third party of Gregor Townsend to come between them. The stand-in captain was undoubtedly the ace behind a pack which strove in vain to produce tangible evidence of the sign above them in the East stand: Scottish Power. Both Scottish tries stemmed from the broadened point of attack afforded by Townsend's contentious selection at outside-centre: a touchdown by Kenny Logan that certainly was, and the alleged one that only a Ffyona Campbell would have unashamedly claimed.
Chalmers, who fed off scraps on the back foot, was restricted to defensive duties, which he performed ably enough. The initial supply line from Armstrong was somewhat off its telepathic beam of old, hardly surprising given the intervening passage of time. But Armstrong showed glimpses of his best with the improvised 14th-minute break that showed the underdogs the way forward, and with the unflinching tackling which - as Rob Andrew will doubtless lament when the sick note arrives on his desk - is an occupational requirement, let alone hazard, of life as a professional scrum-half.
The Border Terriers' powers of recovery will not be the only factor that determines whether the old firm report for duty when Italy visit Murrayfield next month. The Board of Scottish selectors have a hard-nosed business decision to make.