"51 million views in 40 hours!! My God!!" Psy tweeted Monday.
His previous hit "Gangnam Style" has gotten nearly 1.5 billion views on YouTube, but it took a month to reach the 100-million milestone, MTV said.
"He set the bar pretty high to match the success of 'Gangnam Style,'" Billboard Director of Charts Silvio Pietroluongo said. "That song had so many elements going for it: It was catchy, it had a spectacular video, the novelty of being in Korean ... it was like lightning in a bottle ... To get close to that would be considered a success. Even a fraction of those numbers would be a success."