Even more impressive than the 20 million total is the "well over 2 million" peak concurrent viewers - that's how many people were tuned in at one time to watch the action as it unfolded in Seattle.
The tournament this year gave gamers more options to view The International - there were multiple languages on offer, newcomer-specific channels, and the ability to watch matches on demand, "spoiler-free".
Plus, y'know, there was the always-present in-game option and - for the first time - television coverage via ESPN.
...but Dota 2 still has a long way to go to catch up with nearest rival League of Legends - the MOBA drew 32 million viewers total in 2013, with 8.5 million peak concurrent viewers of the latest season finals.
Jimmy the Geek