The latest instalment in Microsoft's hit Halo game series launched on Tuesday with sales figures expected to top £125 million in the next 24 hours.
Halo 4, featuring the return of super-soldier Master Chief, went on sale at midnight in 350 stores in Britain and 10,000 worldwide.
Phil Spencer, the head of Microsoft Studios, has called the game "arguably Microsoft’s most important entertainment property".
"Halo is something that we want to continue to invest in. It was all about how do we make sure Halo can grow in importance relative to the other major franchises in entertainment, such as Lord of the Rings and Star Wars," Spencer told USA Today.
Microsoft is pulling out all the stops for the launch, hosting spectacular events in cities from Seattle to London, where Master Chief made a midnight appearance by the Thames.
Microsoft also held a massive event last week in Liechtenstein, where historic landmarks and countryside were transformed into a futuristic Halo-like universe.
The last version of the game made $200 million on launch day in 2010, and Microsoft is aiming to beat that figure.
It launched a five-part YouTube series that has atttracted 30 million views.
The Halo series spearheaded Microsoft's foray into gaming, which began with the 2001 launch of the first Xbox.
It has sold more than 46 million copies and brought in £1.9 billion in revenue for Microsoft in the past decade.
Halo 4 will vie for the title of 2012's top-selling game with Call of Duty: Black Ops 2, which goes on sale next week.
Halo 4 sees Master Chief, the game's laconic, green-armoured protagonist, dealing out death and destruction to evil aliens while on a quest to save his longtime friend Cortana.