Activision Blizzard's Overwatch video game.

Activision Blizzard's Overwatch video game.

Presales for Blizzard Entertainment Inc.’s next World of Warcraft expansion helped boost revenue in the first quarter, though operating income decreased as it rolled out new business lines.

The Irvine-based publisher recorded revenue of $480 million, up 8.3%, driven by pre-purchases of “World of Warcraft: Battle for Azeroth” and revenue from its Overwatch League, which started its inaugural season in January. The esports league is based on its first-person shooter “Overwatch,” which has grown to a $1 billion since its May 2016 release.

Operating income fell 23% to $122 million due to increased costs to operate and market new business initiatives and higher personnel costs across the operation, the company said.

Blizzard attracted more than 38 million monthly average users of its video games, down from 40 million in the previous quarter and 41 million in the same period a year ago.

The results were included in the first quarter financials from Santa Monica parent Activision Blizzard Inc., which recorded revenue of $1.9 billion and operating income of $595 million, or $0.78 per share.

Both sales and profit beat Wall Street expectations.

Blizzard is Orange County’s largest software maker, employing 2,000 in OC and more than 4,000 worldwide.