Sales of Sony's PSP Go, the disc-less version of the PlayStation Portable gaming console, got off to a low-key start in Japan on Sunday.

The handheld gaming device debuted in Japan a month after it hit store shelves in the U.S. and Europe, sold 28,275 units in its first day on sale, according to data from Enterbrain. The company's sales estimate is based on data from 3,500 computer game retailers in Japan.

The PSP has sold 1.7 million units in the year to Oct. 24, putting average daily sales at 5,786 units until shortly before the PSP Go's launch. That puts the PSP Go's sales on Sunday at roughly five times average daily sales. Other recent console refreshes, such as the PS3 slim and the PSP3000, have boosted sales by a greater amount.

The start of sales of the PSP Go didn't measure up to typical game hardware launches, with no major retailers opening their stores early to accommodate customers and stimulate demand.

The PSP Go does away with the UMD storage medium in favor of downloads of new games over the network. That has ruffled the features of some retailers in other countries because they won't benefit from game software sales once customers buy the device.

Last week Sony said sales of PlayStation Portable devices in the July to September quarter totaled 3 million worldwide, down from 3.2 million in the same period of 2008. For its April 2009 to March 2010 financial year the company expects to sell 15 million PlayStation Portable devices.