Tencent's free-to-play shooter CrossFire brought in revenues of nearly $1 billion in 2013, according to research from SuperData.
The SmileGate-developed title brought in over 50 per cent extra revenue than Riot Games' hugely successful MoBA League of Legends - also published by Tencent - which took $624 million last year.
According to the data, Nexton's Dungeon Fighter Online was the third most popular free-to-play title, bringing in $426 million, followed by World of Tanks which took $372 million.
EA's Star Wars: The Old Republic also made the top ten, and is said to have generated $139 million in revenue last year, seemingly backing the publisher's move to turn the MMO free-to-play from a subscription-only model.
Despite losing millions of users, fantasy MMO World of Warcraft generated $213 in microtransaction sales - not including its subscription earnings.
The report noted that during 2013 in the US, the digital free-to-play sector grew by 45 per cent to $2.9 billion, while earnings from subscription-based titles slumped 21 per cent to $1.1bn.