Nintendo sold "just shy of 400,000 units" in its first week in the US, according to data supplied by the NPD Group.
That's about 100,000 units less than the DS managed in its first month, but it should be pointed out that the DS launched in November "and had holiday seasonality and a price differential of about $100", analyst Anita Frazier said.
Super Street Fighter IV 3D was the top selling 3DS game during the period.
There was good news for the original DS, which was the best selling platform in the US in March, shifting over 460,000 units.
Pokemon Black & White were the month's bestselling games, the first moving more than 1.3 million copies and the latter over 1.1 million.
"Pokemon White is the best-selling Pokemon SKU in its debut month at retail of any Pokemon to date, and the Black version is third," said Frazier. "Combined they break previous sales records held by Pokemon Silver and Gold in October 2000."
Charlie Scibetta, Nintendo of America's director of corporate communications, commented: "Both Nintendo 3DS and the Nintendo DS family had a strong month, indicating that Nintendo has something for everyone.
"Nintendo provides people with the best video game experiences, from 3D visuals without special glasses to a touch-screen interface to motion controls."
Wii moved over than 290,000 units in the US in March, a month in which Xbox 360 was again the top selling home console.
Nintendo's Wii successor is set to utilise an entirely new controller and will be more powerful than Xbox 360 and PS3, well-placed international industry sources have told CVG.