KSI prevailed by split decision over fellow YouTuber Logan Paul in the pair's highly anticipated rematch in Los Angeles.
Bragging rights went to KSI on Saturday after two judges scored the fight 57-54 56-55 in his favour, with the other giving Paul a 56-55 victory at Staples Center.
American Paul – coached by former heavyweight champion Shannon Briggs – and Brit KSI, whose real name is Olajide Olatunji, had to settle for a draw in a white-collar bout at Manchester Arena in August 2018, which was the most viewed non-professional boxing match in history.
The internet sensations came together again for KSI v Paul II in front of a star-studded crowd, including Justin Bieber and Ed Sheeran, with millions watching worldwide.
There were plenty of punches thrown, but not many landed in the six-round contest under the California lights.
The pair continued to go toe-to-toe through two rounds, though the fight appeared to spring to life in the fourth.
KSI was sent to the canvas but Paul was deducted two points for punching his opponent while he was on the ground and defenceless, despite being awarded the knockdown.
The final two rounds showcased two fatigued fighters before the clash was decided by the judges, with KSI reduced to tears.
"KSI last time was scared, I was scared to fight. This time I went in, I just kept going and going," KSI told DAZN in the ring afterwards. "Fans saw how much bigger he was, his physique. So I thought screw that! I'm going to work my arse off. I want to thank my team, they've helped me so much. Your boy has done it, I am VICTORIOUS!"
"I've never worked so hard, in the ring and in camp. I was ready and I was on fire. He couldn't deal with my jabs. He kept moving but I got him," KSI added.
Logan said: "You had my respect before the fight, you are one of the toughest people I know. I don't like talking trash, it was all to sell the fight. I was more calm this year, we worked on my conditioning."