SAN FRANCISCO - Black Friday retail sales online this year topped $1 billion for the first time ever as more consumers used the Internet do their early holiday shopping, comScore Inc said on Sunday.

Online sales jumped 26 percent on Black Friday to $1.04 billion from sales of $816 million on the corresponding day last year, according to comScore data.

Amazon.com was the most-visited retail website on Black Friday, and it also posted the highest year-over-year visitor growth rate among the top five retailers. Wal-Mart Stores Inc's website was second, followed by sites run by Best Buy Co., Target Corp. and Apple Inc , comScore noted.

Digital content and subscriptions, including e-books, digital music and video, was the fastest-growing retail category online, with sales up 29 percent versus Black Friday last year, according to comScore data.

E-commerce accounts for less than 10 percent of consumer spending in the United States. However, it is growing much faster than bricks-and-mortar retail as shoppers are lured by low prices, convenience, faster shipping and wide selection.

ShopperTrak, which counts foot traffic in physical retail stores, estimated Black Friday sales of $11.2 billion, down 1.8 percent from the same day last year.

"Online has been around 9 percent of total holiday sales, but it could breach 10 percent for the first time this season," said Scot Wingo, chief executive of ChannelAdvisor, which helps merchants sell more on websites, including Amazon.com and eBay.com.

ComScore expects online retail spending to rise 17 percent to $43.4 billion through the whole holiday season. That is above the 15 percent increase last season and ahead of the retail industry's expectation for a 4.1 percent increase in overall spending this holiday.

It's not clear yet whether strong Black Friday sales online will weaken growth on Cyber Monday, which has been the biggest e-commerce day in the United States in recent years.

"Cyber Monday will be a big day, but not as much of a big day as it has been in the past," said Mia Shernoff, executive vice president for Chase Paymentech, a payment processing unit of J.P. Morgan Chase & Co.. "Faster broadband Internet connections in the office used to drive this. But now many consumers have faster connections at home and smart phones and tablets - they don't have to wait."

Mobile shopping growth

A big source of online shopping growth this holiday season has come from increased use of smart phones, which let people buy online even when they are in physical stores, and by tablet computers, which have spurred more online shopping in the evenings, Wingo and others said.

Mobile devices accounted for 26 percent of visits to retail websites and 16 percent of purchases on Black Friday. That was up from 18.1 percent and 10.3 percent, respectively, on the same day last year, according to International Business Machines , which analyzes online traffic and transactions from 500 U.S. retailers.

Amazon and eBay benefit from increased use of mobile devices for shopping because they are consistently the top two online retail destinations for mobile users, ChannelAdvisor's Wingo said.

Amazon.com was the most visited retail website on Black Friday, with more than 28 million visits, according to Hitwise.

Worth noting: eBay runs one of the largest online marketplaces, rather than being a retailer, so its online traffic was not reported by Hitwise. However, eBay said the volume of mobile transactions on its marketplace jumped 153 percent on Black Friday from a year earlier.

ChannelAdvisor clients' same-store sales on Amazon.com shot up 38 percent on Black Friday, compared with a year earlier. Last year's year-over-year growth was 50 percent.

Client same-store sales on eBay's marketplace rose 31 percent on Black Friday, compared with a year earlier. Last year's year-over-year growth was 15 percent, according to ChannelAdvisor.

Price pressure

While mobile devices may be good for sales, they may not be so good for retail profit margins. Smart phones give shoppers real-time access to product prices online, potentially exacerbating the usual holiday discounting and price wars.

Black Friday online transactions jumped almost 30 percent, but the average ticket price was down more than 11 percent, according to Chase Paymentech, which reports data from its 50 largest e-commerce merchant clients.

"It's driving prices down," Shernoff said. "Consumers are checking prices in stores and showing the retailer, and the retailer will succumb to the lowest price online so they don't lose the consumer."