Gennadiy Golovkin put on an impressive display in Saitama, weathering an early onslaught from Ryota Murata before picking apart his opponent to claim the WBA title.
The 40-year-old Kazakhstani fighter celebrated his birthday yesterday and can now fully enjoy the celebrations with another belt to his name.
Murata came racing out the blocks and put Golovkin under immense pressure in the early rounds, landing some heavy shots in the process.
The 36-year-old Japanese fighter then turned his attention towards landing body shots, and he enjoyed plenty of success between rounds two and four.
However, Golovkin showed his experience to weather the storm, before starting to turn the tide after the halfway mark.
In the sixth round, Golovkin started to go through the gears, and was able to knock his opponent's mouthpiece out with a bruising right hook.
As the rounds ticked on, Golovkin was able to pick apart Murata more and more as he advanced, frequently punishing him with his counter right.
Golovkin continued to improve, and knocked his opponent to the canvas in the ninth round, with Murata's coach throwing in the towel before the referee began the count.
Following what was the 42nd win of his career, Golovkin paid respect to his opponent in his post-fight comments.
"Murata is a true warrior who fought to the very end," Golovkin said.
"He is an Olympic champion, a middleweight champion, and despite what took place in front of his fans, we are extremely happy to have organised this event in Japan."