Dota 2
OpenAI's Dota 2 bot defeated world-top professionals in 1v1 using pure self-play with no imitation learning or tree search.
Excerpt
We’ve created a bot which beats the world’s top professionals at 1v1 matches of Dota 2 under standard tournament rules. The bot learned the game from scratch by self-play, and does not use imitation learning or tree search. This is a step towards building AI systems which accomplish well-defined goals in messy, complicated situations involving real humans.
Read at source: https://openai.com/index/dota-2