Old news feeling fresh.

Michael Rubin, who built a global busi­ness in King of Prus­sia by sell­ing stuff online for big-name retail­ers, says he under­es­ti­mated how huge Inter­net sales would become.

And he tips his hat to Amazon.com Inc. and its chief exec­u­tive offi­cer, Jeff Bezos, for that.

“I actu­ally used to tell peo­ple that I didn’t think e-commerce would be as big as they thought it would be,” Rubin, chief exec­u­tive of GSI Com­merce Inc., told ana­lysts at the UBS Global Media and Com­mu­ni­ca­tions Con­fer­ence this week in New York. “I’m now offi­cially doing my 180.”

GSI runs Web stores for clients such as Toys “R” Us Inc., GNC Corp., Dick’s Sport­ing Goods Inc. and the National Foot­ball League. In recent years, through acqui­si­tions, it has been branch­ing into related online mar­ket­ing businesses.

For­rester Research Inc. esti­mated last year that online sales, exclud­ing travel, could go from $200 bil­lion in 2008 to about $300 bil­lion in 2011.

“I now think that e-commerce is going to be sig­nif­i­cantly big­ger than what anyone’s pro­ject­ing,” Rubin said.

Amazon’s role? Rubin said that his out­size com­peti­tor, par­tic­u­larly by ship­ping “fast and free,” is “break­ing down the bar­ri­ers to buy­ing online.” And that helps every­one sell­ing online.

Ama­zon raked in about $20 bil­lion in sales last year — 20 times GSI’s rev­enue. GSI itself expects a fourth-quarter profit from hol­i­day sales, but it has pro­jected a net loss for the year. In the most recent quar­ter, it lost $9.4 mil­lion on $190 mil­lion in revenue.