Figures released by the NPD Group show that the Nintendo DS managed to outsell its predecessor, the Nintendo 3DS, during its first month on sale in the USA.
The 3DS sold just under 400,000 units during March, but the console did launch with only a few days remaining in the month, so it's hardly a fair comparison. The Nintendo DS also had the record-breaking Pokémon Black/White to thank for some strong sales.
Comparing the launches, NPD Group highlighted that while the 3DS sold less than the DS when it launched, the DS launched in November, and also cost less. If you consider this, it means that the 3DS actually generated more revenue for Nintendo, despite selling less units.