The Google-owned video platform said in a blog post Wednesday that the debate had been watched 124 million times since it took place Sunday. The number represents a 40 percent increase from the viewing figures for the debate, which reached 88 million views.
Many of the viewers watched the event live, with 1.5 million people tuning in concurrently at the debate's peak.
The US presidential election is not just of interest to American citizens, the viewing figures revealed, with many people tuning in from countries all over the world. The country with the highest number of people watching after the US was Canada, followed by Mexico, Australia, the UK and Vietnam.
The final presidential debate is scheduled to take place on October 19 in Las Vegas, Nevada, and YouTube will again stream the event live.