Scotland playmaker Finn Russell was near his masterly best as Tonga were finally overrun, but only after the Pacific islanders led 10-7 in the first half and closed it to 24-17 early in the second with a bulldozing charge by 151kg captain Ben Tameifuna, the heaviest man at the World Cup.
Scotland wing Duhan van der Merwe bounced back from a couple of juddering hits on him by Tonga to throw his own considerable weight around in Sunday's (Monday AEST) enjoyable clash.
He scored the second of Scotland's four first-half tries untouched on the left wing, then powered past and through three defenders to set up replacement George Horne in the corner for the try that ended Tonga's resistance and put the Scots 31-17 up with 25 minutes to go.
Fullback Blair Kinghorn added a sixth try, set up by the irrepressible Russell, while replacement Darcy Graham zoomed away for the seventh from 55 metres out in the last play of the game.
Tonga were down to 14 men at that point after a yellow card for No.8 Vaea Fifita for charging into Russell's head at a breakdown, a hit that was put on review and might be upgraded to red after the game.
Scotland face Romania next in pool B, where another bonus-point win is expected to leave them within reach of the quarter-finals if they can pull off a shock against top-ranked Ireland in the last round of games.
Hooker George Turner was at the back of a Scotland maul that travelled nearly 20 meters for the first try in the fifth minute.
Tonga's first comeback came through right wing Solomone Kata's try down the right side, but van der Merwe, fellow wing Kyle Steyn and flanker Rory Darge sealed the Scottish bonus point by halftime.
Tameifuna's rumble three minutes into the second half, taking three Scottish defenders over the tryline with him, turned out to be the last blow Tonga landed as Scotland had all the territory, most of the possession and the last 21 points of the game after halftime.
