In a video clip available online since Sunday the 27-year-old Swede, whose real name is Felix Kjellberg, can be heard using the N-word in an expletive-laden tirade at his opponent.
In a new YouTube video posted on Tuesday that was viewed more than 4.7 million times within 15 hours, Kjellberg said he was sorry.
"You probably won't believe me when I say this, but every time I go online and hear other players use the same kind of language that I did I always find it extremely immature and stupid, and I hate how I now personally fed into that part of gaming," he said.
"It was something that I said in the heat of the moment. I said the worst word I could possibly think of and it just sort of slipped out."
"I'm not going to make any excuses as to why it did, because there are no excuses for it."
PewDiePie is known for posting humorous clips and playing livestreamed video games for his more than 57 million followers on YouTube, making him the site's most watched user.
It is not the first time Kjellberg has been at the centre of controversy. In February he lost contracts with YouTube and Disney over anti-Semitic comments (for which he also apologized), and he was temporarily blocked from Twitter in September 2016 after joking he had joined the Islamic State group.
"I'm disappointed in myself because it seems like I've learned nothing from all these past controversies," Kjellberg said.
"I'm just an idiot, but that doesn't make what I said or how I said it okay. It was not okay," he added.
"I'm really sorry if I offended, hurt or disappointed anyone with all of this."