With many retailers aggressively boasting cut-price offers on the latest in the best-selling FPS franchise, it's little wonder the title has taken the top spot in just two days of sales.
But it's not the only new entry in the chart - after boasting the biggest UK retail launch ever (with 2,000 fans swamping HMV's midnight launch in London), World of Warcraft expansion Wrath of the Lich King enters at number two.
Football Manager 2009 is another new entry, in at third.
That means last week's one and two, Gears of War 2 and FIFA 09, have to settle for fourth and fifth place.
Elsewhere, Guitar Hero World Tour leaps up the charts to number six (up from 17), thanks to Friday's release of the current-gen versions - the PS2 version follows this week.
Conversely, Fallout 3 also took a tumble down the chart, from three to 14.
Konami's Pro Evo 2009, meanwhile, holds firm at 9.
It wasn't exactly the best weekend for new IP, either, it seems - LittleBigPlanet fell from fourth to 19, family/party game Wii Music was a new entry and 16, and EA's innovative FPS Mirror's Edge hit 20th. Nintendo's Professor Layton and the Curious Village meanwhile was stable, falling just one place to seven.
The Gfk ChartTrack UK All Formats Top 10 for this week in full:
1. Call of Duty: World at War
2. World of Warcraft: Wrath of the Lich King
3. Football Manager 2009
4. Gears of War 2
5. FIFA 09
6. Guitar Hero: World Tour
7. Professor Layton and the Curious Village
8. Mario Kart Wii
9. Pro Evolution Soccer 2009
10. WWE Smackdown vs Raw 2009