They got the job done with the win and the bonus point which at least keeps them in the conversation about who is going to qualify from this trickiest of pools into the World Cup quarter-final, but it wasn't a completely convincing performance from Scotland.

They left several chances on the park which could come back to haunt them if they do manage to beat Romania and Ireland with sufficient bonus points to make it a three-way tie at the end of the pool stage, in which case it will come down to points differential. Scotland are currently on +13, which  is an awful long way behind the +122 of Ireland and the +86 of South Africa.

The big concern is the loss of captain Jamie Ritchie before half-time with a head injury. The flanker looked groggy as he made his way from the pitch following a collision with Afusipa Taumpepeau, and while he was likely to be rested next week against Romania, the 12-day stand-down rule makes him a doubt for that Irish showdown, when his leadership, aggression and never-say-die attitude would be key to causing an upset.

Scotland missed an early opportunity to settle nerves when Blair Kinghorn kicked turnover possession 60 yards down field from just outside his own 22, and then won footrace to the ball as it bounced tantalisingly towards the try-line, but the timing just wasn't quite right, and the flying full-back overshot his target before it entered the in-gaol area.

It didn't, however, prove to be a costly miscalculation, because just two minutes later, a line-out maul thundered a full 20-yards for hooker George Turner to get the opening score, with Finn Russell slotting the fairly easy conversion.

Tonga bit back when William Havili slotted a long-range scrum penalty, given against Rory Sutherland whose knee had hit the deck.

Scotland were cutting some nice shapes across the backline against a far less oppressive defence than they encountered a fortnight ago in Marseilles, but Duhan van der Merwe bouncing off Solomone Kata's shoulder like a rubber ball, and a big hit in the middle of the park on Sione Tuipulotu by opposite number Pita Ahki, served as timely reminders of Tonga's physical threat.

The Pacific Islanders then demonstrated their attacking potentials when a sweeping attack and sublime offload from Salesi [previously Charles] Piutau sent Kata over, and Havili's conversion made it 7-10 to the team in red with just over 20 minutes played.

After a tricky time against the Springboks, Russell was back to his ball-on-a-string best, with one excellent 50-22 coming to nothing when the ball was lost at a subsequent ruck, before he nearly released Kyle Steyn on the right with an equally impressive cross-kick, bur this time the busy winger couldn't quite collect under pressure from two defenders, including Havili, who was penalised for a no-arms tackle.

That Scots kicked to touch and when they couldn't get traction with their maul on this occasion, the ball was spread across the park, with Russell and Tiupulotu working that wrap-around move they so love, before Kinghorn sent Duhan van der Merwe over.

No conversion but Scotland were back in front, and this time they kicked on, with Russell's flat pass putting Steyn in space, and he shrugged off a despairing tackle from Ahki on his way to the line. This time the conversion came back off the left post.

Scotland lost Ritchie when he accelerated into contact and was caught by Taumpepeau, who had failed to lower his body height, and in fact lifted his shoulder as it made contact with the Scottish skipper's head. Ritchie looked pretty groggy as he left the pitch and did not return from his HIA, while the Tongan winger was initially yellow-carded, and it came as a bit of a shock when there was no upgrade to a red by the 'Bunker'.

A great chase of Russell's smart kick by Scott Cummings and Matt Fagerson led to Piutau being bundled into touch deep inside his own 22, and it took some heroic Tongan defending to first repel Chris Harris back over the try line on the right, then bundle van der Merwe into touch on the left, before the pressure finally yielded the bonus-point try from Rory Darge, who picked himself cup off the deck in heavy traffic following a tackle in front of the posts and bustled over.

Russell's conversion was the last act of the first half. The job was half done, with that bonus-point in the bag, but Scotland still needed to make absolutely sure of the win ... and boosting their position for a possible points chase to qualify from this pool would be handy, too. 

Tonga served notice that they weren't going down without a fight when they capitalised on some sloppy Scotland play just three minutes after the restart. Ben White hurled a quick line-out to Russell, whose clearance from behind his own line sailed straight towards Kata. The winger ran the ball back with venom then a quick recycle allowed skipper and tight-head prop Ben Tameifuna to build up a head of steam that carried him all the way to the line.

Scotland couldn't get back into their groove. Kinghorn guddled a fairly straight forward kick receipt into touch, Dempsey was penalised for pulling a Tongan  arm down at the line-out and Russell's kicking radar seemed to be on the blink.

They needed a moment and it came from the little-and-large combination of replacement scrum-half George Horne, who scampered home, after van der Merwe had used his considerable strength to shrug off Kata's challenge and turn stagnant possession into something more promising.

Scotland were still some way less than convincing, but they dominated possession and territory for the next 10 minutes, and eventually added to their account when their driving play left Tonga's defence as a ragged red line and Kinghorn ran a nice angle onto Russell's pass.

Van der Merwe set off on a rampaging run straight from the restart, reminiscent of his try against England, but this time his steps inside failed to shake off the cover defence, and when his pass to the supporting Kinghorn floated instead to the less well positioned Huw Jones, the scoring opportunity faded away.

Scotland continued to huff and puff, mostly inside Tonga's 22, and Kinghorn went close again, before Darcy Grahamprovided an injury-time flourish, coming off his wing to take a short ball from a ruck, jinking clear and then racing home from his own 10-metre line, setting up an easy Russell conversion.

At this point, Tonga were down to 14 men following the yellow-carding of  Vaea Fifita for a dangerous clear-out of Russell on 77 minutes, which was upgraded after the final whistle to a red.