According to a just-published NPD Group MusicWatch report for the first quarter of 2007, covering the sales of both physical and downloadable music, Apple’s iTunes has jumped in rank to become the third-largest retailer of music in the United States. iTunes now holds a 9.8% share of music purchases, ahead of fourth place Amazon.com at 6.7% and fifth place Target at 6.6%. Walmart remains the nation’s largest music retailer with a 15.8% share of the market, with Best Buy holding 13.8% for second place.

The MusicWatch findings are especially interesting in that 86.2% of the quarter’s music sales were in a physical (CD) format, versus a 13.8% share in downloadable format. Unlike Wal-Mart and Best Buy, iTunes gained share despite the fact that it only sells downloadable content. It leapfrogged CD-heavy competitor Amazon to gain fourth place in January.