It looks like marketing efforts and price cuts are paying off for the Nintendo 3DS. According to market research firm The NPD Group’s October 2011 analysis, the 3DS  has sold 1.65 million units since launching in the US in March, making it viable that the system could beat out its predecessor, the DS, in first-year sales.

Nintendo’s portable 3D device was the second best-selling hardware platform, with combined 3DS/DS sales up over 25% from last year. October weekly unit sales of 3DS and DS platforms also saw an increase over September 2011.

The Xbox 360, meanwhile, was the top-selling hardware platform for the month, realizing a unit sales increase of more than 20% versus the same time last year.

The ongoing trend of integrating physical toys with gaming software is also gaining traction. Skylanders: Spyro’s Adventure, which features integration with physical toys, came in just outside the top 10, ranking #11 in new physical unit sales for the month of October.

Still, based on historical seasonality trends, new physical sales of hardware, software and accessories should come in flat to down by as much as 2% once full year sales are in. Interestingly, NPD found that accessory sales have declined since last year, especially among gamepads and specialty controllers.