Ulster video gamers were amongst thousands of fans across Europe who got their hands on the eagerly anticipated Halo 3 at midnight.
Stores throughout the province were among up to 1,000 UK shops that opened late for the launch of the Xbox 360 game yesterday.
Halo 3 is the final instalment of the video game and is expected to outsell any new DVD release this year.
Microsoft expects its first week of revenue from Halo 3 sales to outstrip that of blockbuster films such as Harry Potter.
Una McCaffrey, assistant manager at HMV in Donegall Arcade, Belfast, said extra staff had been drafted in to deal with the event.
"It is the biggest launch of the year and it is also expected to exceed any DVD new release to date of this year," she said.
"So, basically, it is the biggest thing that we are going to see here to date.
"Every main game shop in the Belfast city centre area will be open late, as well as stores in Derry and Bangor."
She added: "The previous Halo games have been hugely popular with amazing graphics.
"So we are preparing to be very busy from midnight onwards."
Global pre-orders for Halo 3 have passed the 1.25 million mark, according to Microsoft.
It has become a major entertainment franchise in recent years - with spin-off games, clothing, novels and action figures all available.
John Haulihan, spokesman for gaming website www.computerandvideogames.com, said Halo was the "figurehead" game for the Xbox console. " This is the third part of a trilogy and it is going to wrap up all the story line," he said.
Halo 3 is based in a time when mankind is on the brink of extinction. Players take on the role of the last survivor of a secret military project who has to fight to save humanity. It is priced at around £44.99.