Flanker Blair Cowan, fullback Stuart Hogg, centre Alex Dunbar, prop Geoff Cross and wing Tommy Seymour scored the tries and scrumhalf Greig Laidlaw kicked 12 points as the Scots earned their second victory in three November test matches.
Tonga flyhalf Latiume Fosita converted four penalties, punishing Scottish maul infringements, to put the visitors 12-7 ahead after half an hour before Hogg’s breakaway try gave the hosts a 14-12 halftime lead.
Both sides had a player sinbinned, Tonga flanker Nili Latu and Scotland’s Dunbar, in the first half of the match, played on the artificial pitch at Kilmarnock FC’s Rugby Park.
Scotland began the test window with a 41-31 win over Argentina before losing to New Zealand 24-16 last weekend. Tonga were fresh from wins over Georgia and the United States.
“I think the guys can take a lot of confidence from that (second half),” head coach Vern Cotter, who has breathed new life into a Scotland side beaten 21-15 by the Pacific Islanders two years ago, told the BBC.
“(But) if we come back thinking we can reproduce the same stuff (in the Six Nations), that’s a trap, that’s dangerous.”
Scotland replied to Fosita’s early penalty when New Zealand-born man-of-the-match Cowan went over from a maul after 13 minutes during Latu’s spell in the sin bin.
The home side gave away numerous penalties in the first half though, allowing Fosita to rack up points with a perfect kicking performance, his fourth success coming after Dunbar was shown the yellow card for a dangerous tackle.
However, Hogg was quick to pick up the loose ball at a tackle with Scotland defending deep inside their 22 and he ran the length of the pitch to level the score at 12-12 before Laidlaw’s second conversion gave them a narrow halftime lead.
Fosita missed a penalty early in the second half before flyhalf Finn Russell attacked down the blindside in the 48th minute and passed to Dunbar who broke through two tackles to touch down in the corner.
It was the signal for the Scots to dominate the rest of the match.
Laidlaw added two penalties before Cross broke over the Tongan line in a maul in the 67th minute and Seymour put the icing on the cake with his third try in three tests, touching down from Russell’s chip into the goal area.
(Reporting by Rex Gowar in London; Editing by Ian Chadband)