Naoya Inoue successfully defended his undisputed super-bantamweight championship with a close but uncontroversial 12-round unanimous decision over Junto Nakatani in their eagerly anticipated showdown at the Tokyo Dome on Saturday night.

Before a sellout crowd of about 55,000 spectators during Japan’s Golden Week holiday, Inoue held off a fierce late surge from his unbeaten rival to win by scores of 116-112, 116-112 and 115-113 and retain the WBA, WBC, IBF and WBO belts at 122lb, extending his perfect record in what had been billed as the biggest fight in Japanese boxing history. (The Guardian had it 115-113 for Inoue.)

The four-division world champion nicknamed the Monster had spoken during fight week about wanting to “prove that I’m still Naoya Inoue”, perhaps a nod to the whispers of his purported decline. But the 33-year-old showed why he remains one of the world’s best fighters regardless of weight – if not the outright pound-for-pound king – by getting the better of a taller, longer, younger challenger seen as his most dangerous opponent in years.

“I’m 33 now and I was fighting against a Japanese fighter who’s coming up in the pound-for-pound rankings, so I was determined not to lose,” Inoue said afterwards. “It was different to the fights I’ve had before, with the pressure. So I’m relieved that I won.”

From the opening bell, the magnitude of the occasion seemed to settle over the arena. The vast dome fell under an almost complete silence in the first round, the crowd absorbed by both fighters as they took one another’s measure. Inoue was the first to impose himself, edging forward behind a sharp jab that allowed him to slip inside and disrupt Nakatani’s rhythm. The challenger spent much of the round on the back foot, briefly thrown off balance at one point. While few punches landed cleanly, the early initiative belonged to the champion.

That pattern held through the opening frames. Inoue’s hand speed and footwork were immediately apparent, his ability to dart in and out of range giving Nakatani pause. Both men probed with the jab through the third with Nakatani looking to counter when Inoue stepped into the pocket, but the exchanges largely favored the champion.

“Naoya is quite good learner,” Nakatani later said when pressed on his passive opening, which saw all three ringside judges score the first four rounds for Inoue. “He learns a lot in such a short period of time. I didn’t want to disclose everything I had in the early rounds, so that’s why I fought that way.”

The fight settled into a tactical rhythm through the middle stages. Nakatani appeared reluctant to commit fully, wary of what might come back, while Inoue gradually increased the pace, landing the more telling shots. By the fifth, Nakatani produced his best work to that point. It was a reminder that the fight was far from one-sided, even as Inoue continued to edge ahead on the scorecards.

Each time Nakatani threatened to build momentum, Inoue had an answer. When the challenger found space to work in the sixth, the champion responded in kind, snapping back combinations with precision and authority. Yet Nakatani was beginning to step forward more and take on risks that he had avoided earlier.

Sensing he was behind in the seventh, Nakatani pressed the action, forcing exchanges and drawing the crowd into the action. The eighth was the most compelling round to that point, both men letting their hands go in sustained firefights. Inoue’s jab remained a stabilizing force, repeatedly halting Nakatani’s attempts to impose himself, but the younger fighter’s renewed sense of urgency was unmistakable.

It paid off for him in the ninth as Nakatani surged, backing Inoue up and working in combinations with increasing confidence. A sharp uppercut followed by a left hand punctuated a strong round and he carried that momentum into a furious 10th, throwing with abandon and landing punishing blows as Inoue was forced on to the defensive in ways few of his opponents have managed.

Then came the accidental clash of heads that left Nakatani with blood streaming down his face. As he tried to soldier through it, Inoue planted his feet and met him with a heavy right hand, then a crisp uppercut that snapped the challenger’s head back. With blood from the cut increasingly affecting Nakatani, Inoue reasserted control with the finishing kick of a champion.

Defeat does little to diminish Nakatani’s standing. The three-division champion demonstrated resilience, adaptability and a willingness to push one of the sport’s best fighters to the limit. Against most opponents, his second-half rally might have been enough. But Inoue is not most fighters.

“I prepared for lots of different eventualities so I wasn’t really surprised by the way he fought,” Nakatani said. “But he fought like a champion and he’s a great boxer.”

Having defended the super-bantamweight titles for a seventh time, Inoue tightens his grip on the 122lb division and writes another chapter in a sparkling career that had crossed the Hall of Fame threshold many years ago. And while it may seem there are vanishingly few worlds left for him to conquer, a showdown with unified 115lb champion Jesse “Bam” Rodriguez already has fans abuzz.

“I had four fights last year and then here at the Tokyo Dome tonight and that has taken its toll, so please let me rest for a while now,” Inoue said. “After that, I’ll come back and speak to my team and organize another fight that everyone can get excited about.”