The Islanders muscled their way back into the match with four second half tries after going into the break 20-4 behind only for Scotland full-back Matty Russell to deny them with the winning score nine minutes from the end of an epic match.
Tonga looked formidable during their pre-match Sipi Tau war dance and they carried that warrior spirit into the opening exchanges of the match. Scotland, finding themselves forced back onto their own line, could do nothing as Glen Fisiiaha broke clear to open the scoring after some fine build up play.
The setback brought a strong response from the Bravehearts who pushed Tonga back by working hard as a unit with real endeavour. It looked as though their efforts would return fruitless until Russell found the strength to bulldoze his way through the grasps of several Tongan tacklers and slide over the line for his first try. Captain Danny Brough landed the goal and Scotland were 6-4 ahead.
The match slowed to a halt when Ben Murdoch-Masila left the field injured after a heavy fall, but it soon picked up pace. Scotland forced a penalty midway through the Tongan half and Brough sent his kick between the posts to extend their lead.
Great tenacity in defence by the Scots epitomised their approach to the game and they carried it into attack as well. Ben Fisher collected the ball after good pressure and when his kick through was missed by Fisiiaha the hooker pounced for a try converted by Brough.
Fisiiaha looked nervous after his mistake and another fumble from a clearance kick created the position from which Scotland stretched their advantage with a try by Brett Carter from Danny Addys fine one-handed pass.
Brough's kick ricocheted off an upright and over to open up a 16-point interval lead and send the biggest crowd seen at Workington for decades into raptures.
Tonga had gone into the tournament as dark horses and they demonstrated why following the restart with an irresistible passage of play to claw their way in front going into the final quarter.
The fightback began when a bouncing ball was met expertly by the onrushing Sika Manu who dragged three Scotsmen with him over the line for Samisoni Langi to add the conversion.
Fuelled with confidence, Tonga poured forward and the powerful Fuifui Moimoi surged clear, before laying the ball to Nafe Seluini who darted between the Scots' backs and touched down.
Increased pressure kept Scotland penned back on their line and after two near-misses, Tonga made another breakthrough when Sika Manu got his fingertips to a loose ball for a try. Langis goal would have levelled the scores but his kick flew high and wide.
Tonga were in no mood to be denied, however, and there was an air of inevitability when Willie Manu sent them into the lead after brilliant teamwork to cut through a faltering Scottish defence for Langi to kick the goal.
What could have been a crushing blow for the Bravehearts instead brought a magnificent response and quickfire handling in front of the Tonga line led to Russell powering over for his second try to level the scores.
Brough, the Super League Man of Steel, showed steely nerves to land the telling goal and end the scoring on a night that will be talked about in Cumbria for many years to come.