Facing a side of powerful runners packed with experience in both the Super League and NRL, the Bravehearts did not take a backwards step and got their just rewards at Derwent Park in Workington.
Priced as long as 8/1 beforehand, McCormack's men gave the Cumbrian fans a taste of what top-flight rugby can be like - which will no doubt have fuelled their desire to have a side in the Super League.
For now, though, they can feast on Scotland's heroics, with schoolteacher McCormack enjoying the best possible time off work as his side galvanised themselves sufficiently after squandering a 16-point lead to win it.
Even then they had to endure a last-second video referee decision - a sixth of the night - to get the job done.
It was fine news for the packed-out crowd - the demand to join was so high that some fans had to be housed in an end which was not intended to be used - who were in for a treat from the off as Tonga set the tone with a rousing Sipi Tau haka.
Their enthusiasm drew a 37-second knock-on out of Scotland's Adam Walker and after a couple of settling-in plays they took an eighth-minute lead as Sika Manu's delayed ball put full-back Glen Fifi'iahi through.
Scotland's response was a fine one, though, and one they could have been forgiven for not making considering the early battering they were getting from brutish prop FuiFui MoiMoi.
A short kick-off from Danny Brough got them the ball back and after Konrad Hurrell coughed up possession in the next set, Russell dragged his way out of three would-be tacklers to score.
Brough upgraded the try and then tagged a penalty, with a tasty punch-up between the two sides in the meantime keeping the fans enthralled.
Tonga returned with interest and Sosaia Feki was dragged in touch as he bore down on the corner, while Brett Carter - a local favourite as a Workington player - was guilty of taking his eye off the ball in an identical position.
He was bailed out by substitute hooker Ben Fisher, though, who scored Scotland's second try with 32 minutes gone.
The retiring nine kicked ahead and his energy on the chase was rewarded as Fisi'iahi failed to gather the ball. Brough turned it into a six-point gift.
There was only one side in it, with Tonga apparently already out of steam, and as half-time approached, a third score arrived.
Fisi'iahi again fluffed his lines and from the subsequent set, Danny Addy's fine pass put Carter in for the most popular of 'home' scores. Scotland's fortunes were summed up as Brough landed the touchline goal, with the ball bouncing off the bar and dropping over.
Scotland took that score to the dressing rooms but Manu chipped away at the deficit immediately after the restart as he snaffled up a kick which reared up above Brough, giving Samsoni Langi an easy conversion.
Tonga's roll continued apace and Nafe Seluini went over from close range after a string of Scottish errors, while another try was wiped out when Daniel Tupou was punished for a double movement.
Scotland were in tatters at the back and all Tonga were having to do was kick in goal to cause havoc. That tactic paid off with 55 minutes gone as Manu grounded a Daniel Foster kick with his fingertip but another failed conversion left Scotland two points ahead.
That almost changed as Danny Addy spat out possession to give Ukuma Ta'ai a free run but his knock-on cost Tonga another score, although that only delayed the inevitable.
With 13 minutes left, a desperate, last-tackle hack from Foster was there for Ben Hellewell to catch but it hit him on the head, skipped off and eventually came to Willie Manu to run clear.
But Scotland were not done and somehow found a way to win it.
Russell did as he had done in the first half, with Brough giving Scotland a two-point lead which they preserved.