In front of a 28,728-strong pro-Tongan crowd at CommBank Stadium on Sunday, the Kangaroos made amends for last year's final - when they suffered the biggest defeat in their history at the hands of New Zealand.
Tom Trbojevic grabbed two tries at centre but it was Dearden who shone brightest as he upstaged halfback Mitchell Moses on his home ground, showing a ruthless edge to exploit Tonga's defensive lapses.
If it weren't for injuries to Nathan Cleary and Cameron Munster, the North Queensland playmaker may have been relegated to a bit-part role during this tournament.
But his man-of-the-match performance against Tonga has now given Mal Meninga a major headache as he looks ahead to next year's Ashes series against England.
Australian flyer Xavier Coates was among the Kangaroos' try scorers. (Mark Evans/AAP PHOTOS)
"His confidence has grown over three games, and his belief that he belongs in this arena," Meninga said.
"He belongs in that No. 6 jersey and he was outstanding today.
"But it's all around Tom, believing in Tom and once he gets that on a regular basis, he's going to be a terrific player.
"Sometimes it takes players a while to believe that they belong in this environment."
The Tongans, fresh off last week's upset win over the Kiwis, threatened to cause another boilover when they scored with seven minutes left to close the gap to six points.
But Kristian Woolf's side had lacked the same level of composure as their Australian rivals after taking an early lead.
"I'm very proud of our blokes, I thought our effort was outstanding, and that's the only thing I can ask for," Woolf said.
"There were chances that we didn't get right and that makes it a little bit different.We just didn't quite execute."
Tom Trbojevic scored a double in the minutes either side of halftime. (Mark Evans/AAP PHOTOS)
Halfback Isaiya Katoa was the architect of his side's sixth-minute opener, crabbing across field to set up Sione Katoa, who sent the hymn-singing Tongan crowd wild.
The Tongan No.7 couldn't make the conversion and was offline with the boot again soon after, allowing Australia the opportunity to post a response.
A last-tackle bomb was gobbled up by Trbojevic and the Kangaroos raced up field with Hamiso Tabuai-Fidow touching down in the corner.
"I'm really proud of Isaiya from this tournament," Woolf added.
"He hasn't got everything right and he's a really hard marker on himself.
"He's only going to get better from this and I've seen the way he's grown up through this tournament."
After Tonga winger Daniel Tupou had a try chalked off for obstruction, the Kangaroos settled and pushed further in front when Lehi Hopoate was dragged into his own in-goal.
On the following set, Australia went to the left through the lively Dearden and found Xavier Coates in the corner.
Dearden was the architect for Australia's next when the North Queensland playmaker pinballed through Taniela Paseka and Soni Luke in centre-field.
Trbojevic was backing up in support and touched down under the posts.
The Manly fullback was held up twice in the final two minutes of the first half by Tonga's scrambling defence that restricted the Kangaroos' halftime lead to 14-4.
But any glimmer of hope Tonga could claw their way back into the game quickly dissipated when centre Paul Alamoti reeled out a tackle with a dislocated elbow.
Sensing Alamoti was vulnerable, Dearden showed great awareness to attack the gap where the Tongan centre ought to have been defending to send Trbojevic in for his second.
Australia were on the brink of running away with the game until Tui Lolohea sent in a well-weighted in-goal grubber that was dotted down by Haumole Olakau'atu.
Eli Katoa crashed over in the 73rd minute to cut the Kangaroos' lead to six points but Tonga could not land a final blow to send the game to golden point.
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