NEW YORK (CNNMoney.com) - Black Friday was the unofficial start of the 2005 holiday shopping season, but one report issued Monday said sales were not so jolly.

Sales for the season's first two days dipped 0.5 percent as compared to the same two-day period in 2004, according to ShopperTrak's National Retail Sales Estimate.

Combined Black Friday and Black Saturday sales totaled $13.41 billion versus the $13.48 billion posted in 2004, the retail tracking firm said.

Some consumers may be taking advantage of the extra Saturday this holiday season and beginning their shopping later in the season, the report suggested.

"It seems safe to say that the flat performance we saw this weekend is not necessarily going to be indicative of the holiday season as a whole, as traditionally Thanksgiving weekend is not a bellwether of consumer spending throughout the entire season," Michael Niemira, chief economist and director of research for the International Council of Shopping Centers, said in a statement.

"The industry can expect to see much healthier sales patterns as we move into December and closer to both Christmas and the annually strong Saturday before Christmas retail boom," he added.

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