Marty Cortinas

SPECIAL FOR USA TODAY

SAN FRANCISCO -- The prize pool for the annual championship for the battle-arena video game Dota 2 hit $10 million this week, making it by far the largest e-sports event and moving it ahead of the Masters golf tournament.

Dota 2 is an online game pitting two teams of five players against each other. According to the game's developer, Valve, there were about 8 million unique Dota players in the past month.

Unlike traditional sports tournaments, the majority of the prize pool for the 2014 International comes directly from fans of the game. Valve seeded the pool with a $1.6 million contribution. In May, the company put The International Compendium, an interactive event program, up for sale. The Compendium costs $10, and $2.50 of each sale goes to the prize pool.

Players can level up their Compendiums to get in-game rewards by making predictions, playing matches and purchasing points. In return, they get several in-game perks and items. Players have spent more than $30 million on the Compendium through direct sales and point purchases, bumping The International prize pool by $8.4 million.

"Our goals are to connect the audience with the event in as many interesting ways as we can think of, and reward the players for the value they bring to the Dota 2 community," said Erik Johnson, Valve's market director of operations. "So it's fantastic to see the community so engaged with the tournament, and driving up the prize pool so much."

Valve has pushed the pool along by offering numerous rewards for hitting stretch goals. Apparently even Valve was surprised by the level of support from the fans -- the original goals stopped at $6 million, and the company quickly announced a second round that covers up to $10 million in the pool.

The pool will continue to grow until The International kicks off in July in Seattle. The 19 qualified teams from around the globe will battle starting July 8 for the eight slots in the final event, to be held at the 17,000-capacity KeyArena July 18-21. Tickets (starting at $99) for the event were sold out in within an hour of being put up for sale in early April.

The current $10 million pool far surpasses the previous e-sports record holder, the 2013 International. Using the same funding plan -- $1.6 million from Valve plus Compendium proceeds -- 2013 International had a prize fund of $2.9 million. The only other e-sports competition with a prize pool of more than $2 million was the League of Legends Season 3 Championship, with $2.05 million.

Valve has given organizers the opportunity to create their own Compendiums for other Dota 2 tournaments. "Some of those tournaments have tripled the total prize pool, and since we've added the feature there has been a little over $700,000 contributed to tournaments other than our own," Johnson said.

The 2014 Masters golf tournament had a prize fund of $9 million. Dota 2 has a long way to go before overtaking tennis, however. The 2013 U.S. Open had a prize fund of $32 million.