World Cup - Tonga triumph over Japan
Tonga's hulking forward pack enjoyed total dominance during the scrum and the breakdown proved a fruitful source of possession as their obvious physical advantage proved too much at the Northland Events Centre.
Both sides ran in three tries but it was the kicking of fly-half Kurt Morath that proved the difference as, despite a lack of discipline and poor decision-making in the team, his 16 points with the boot helped overcome the Pacific Nations champions.
If that proves too tall an order, the result - their first win in the tournament - boosts their chances of finishing third in Group A and qualifying for the 2015 tournament in England.
"It's better to beat them here than at the Pacific Nations," Tonga coach Isitolo Maka said, referring to his team's loss to Japan at the Pacific Nations Cup in July.
"It means more here. This win has lifted all of us."
The Tongan forwards tore into their opponents from the kick-off after Japan captain Takashi Kikutani spilled the ball from a huge hit in his own 22 in the opening play.
Six minutes of Tongan pressure followed before number eight Viliami Ma'afu drove over from short range after the Japan scrum had been wheeled towards the touchline under immense pressure.
The Japanese forwards looked rattled but bounced back from their early roughing up to snatch a try with their first attack in the 14th minute through Kensuke Hatakeyama.
The prop picked and drove over from the back of a ruck on the Tongan line and, despite appearing to make a double movement, was awarded the score by the video referee.
Tonga, however, replied instantly when lock Tukulua Lokotui was on hand to run in an easy overlap after the ball had popped out of the ruck on the Tongan side from the restart.
Japan replied once again when slack Tongan defending allowed inside centre Ryan Nicholas to break through and, after quick recycled ball and another slick handling move, flanker Michael Leitch powered over in the corner in the 26th minute.
The two sides gave away 27 penalties between them and Morath was on form with the boot and slotted another two minutes later to extend the lead.
"The breakdown was the difference," said Japan coach John Kirwan. "Obviously it's very disappointing but Tonga were very physical and we had too many turnovers."
Morath's counterpart James Arlidge had a poor evening. He failed to convert the opening two tries and was sin-binned in the 31st minute after racing into an offside position to intercept a pass as Tonga threatened once again.
Morath kicked the three points to extend the lead to 18-10 but despite being a man down, full-back Shaun Webb kicked a penalty just before the break for Japan's 'Brave Blossoms' to close the gap to five.
Tonga ran in their third try in the 54th minute when winger Fetu'u Vainikolo cut inside and barged through a poor tackle by Arlidge to score with Morath converting to stretch the lead to 28-13.
But ill discipline cost the Pacific Islanders as replacement prop Halani Aulika was shown a yellow card with 20 minutes to go after Tonga were deemed guilty of persistent offending by English referee Dave Pearson.
Japan made the most of the numerical advantage and centre Alisi Tupuailai cut back on a sharp line to crash over and close the gap but Arlidge missed again with the conversion.
With captain Lutui off the field, Morath slotted his fourth penalty for a 31-18 lead in the 67th minute as Tonga opted for the kick rather than go for a fourth try and bonus point.
A fire then broke out with 10 minutes to go behind the stadium which was quickly dealt with by a fire crew as Tonga, despite losing lock Lokotui to the sin bin, held off Japan's bid for a losing bonus point.
"The game itself was so tough. We apologise for not being able to win," Kikutani said in a pitchside interview. "We will keep up our good work against Canada, we will never give up."
Japan were seeking only a second World Cup win ever - their last came over Zimbabwe in 1991, before 16 consecutive defeats.
7' Ma'afu try: Tonga 5-0
14' Hatakeyama try: 5-5
16' Lokotui try: Tonga 10-5
17' Morath conversion: Tonga 12-5
26' Leitch try: Tonga 12-10
29' Morath penalty: Tonga 15-10
32' Morath penalty: Tonga 18-10
39' Webb penalty: Tonga 18-13
49' Morath penalty: Tonga 21-13
55' Vainikolo try: Tonga 26-13
56' Morath conversion: Tonga 28-13
63' Tupuailai try: Tonga 28-18
68' Morath penalty: Tonga 31-18