Blizzard's science fiction real-time strategy game StarCraft II: Wings of Liberty obliterated sales of all other games released in the US in July, NPD said.
It sold an eye-watering 721,000 units at retail. StarCraft II was released on 27th July, so those sales were achieved in just five days.
StarCraft II is the fastest-selling strategy game ever.
According to Blizzard's stats, it sold more than 1 million copies in 24 hours, and over 1.5 million copies in 48 hours, worldwide.
StarCraft II helped increase US PC game sales by a whopping 103 per cent for July, according to NPD.
Elsewhere, the Xbox 360 and PS3 versions of EA's NCAA Football 11 came in at second and third with a combined 692,000 units sold.
Scottish developer Ruffian will be celebrating after its Xbox 360 exclusive Crackdown 2 placed fourth, ahead of Super Mario Galaxy 2, the DS version of LEGO Harry Potter: Years 1-4, Red Dead Redemption on Xbox 360 and the Wii version of LEGO Harry Potter.
Square Enix will also be clinking champagne glasses after the superb Dragon Quest IX: Sentinels of the Starry Skies came in at nine.