U.S. shoppers spent $9.74 billion on Black Friday, the day after Thanksgiving. That’s a drop of 13.2 percent compared with last year, according to data released on Saturday by research firm ShopperTrak.

The decline appears to show that more Americans shopped on the holiday itself: Combined spending on Thanksgiving and Black Friday, which had been considered the official start to the holiday buying season until this year, rose 2.3 percent to $12.3 billion.

The data reflects that Thanksgiving, which along with Christmas was one of two days a year that most stores were closed, is becoming an important day for major retailers.

Black Friday is a time when big retailers open early and offer deep discounts, but a few started opening and offering those discounts on Thanksgiving a couple years ago. And this year, at least a dozen did so, with a few opening earlier in the holiday than they did last year.

The National Retail Federation, a retail trade group, predicted that 33 million, or almost a quarter, of the 140 million people who planned to shop during the four-day holiday weekend that ends on Sunday, would do so on Thanksgiving. Analysts had questioned whether the holiday openings would steal sales away from Black Friday or result in people spending more overall.

“Retailers were pretty successful in drawing the consumers into the stores on Thursday,” said ShopperTrak founder Bill Martin, whose company counts how many shoppers go into about 40,000 stores in U.S. But “Thursday’s sales came at the expense of Black Friday’s numbers.”

The decline in sales on Black Friday was the second one in a row. Last year, sales on that day dropped 1.8 percent to $11.2 billion, though it still was the biggest shopping day last year, according to ShopperTrak.

Despite the big drop this year, Shoppertrak’s Martin said he thinks Black Friday will remain the biggest shopping day of the year for the 10th consecutive year. But if retailers continue to promote Thanksgiving as the start of the holiday buying season, he thinks the holiday will eventually surpass Black Friday in sales.

“We’re just taking Black Friday sales and spreading them across a larger number of days,” Martin said.

There will be a clearer picture of sales for the first holiday shopping weekend on Sunday when The National Retail Federation releases data.

Overall, the retail trade group expects sales to be up 3.9 percent to $602 billion for the season, which encompasses the last two months of the year. That’s higher than last year’s 3.5 percent growth, but below the 6 percent pace seen before the recession.

Some retailers said the holiday shopping season is off to a good start. Wal-Mart, the world’s largest retailer, said it sold 2 million TVs and 1.4 million tablets on the Thanksgiving, while Macy’s said 15,000 people showed up to the 8 p.m. opening of its flagship New York City store on the holiday.

Edwin Molina, 30, a New Yorker who works in construction, waited with his wife in line for an hour at a Best Buy that opened at 6 p.m. on Thanksgiving. He said he likes the holiday openings. “It was better, less hectic,” he said.

But not everyone liked the earlier start to the shopping season. Workers’ rights groups and some shoppers led small protests to decry the way some store employees had to miss holiday meals at home.

And as his wife shopped in a mall near Atlanta on Black Friday, Curtis Akins, 51, sat on a bench, lamenting the holiday openings.

“It’s taking away from the traditional Thanksgiving,” Akins said.

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By Steve Rothwell. AP reporters Jeff Martin and Mae Anderson contributed to this report.