Bye-bye Black Friday. So long Small Business Saturday. Now, it's Cyber Monday's turn.

It's estimated that this year's Cyber Monday will be the biggest online shopping day of the year for the third year in a row: According to research firm comScore, Americans are expected to spend $1.5 billion, up 20 percent from last year on Cyber Monday, as retailers have ramped up their deals to get shoppers to click on their websites.

Cyber Monday specials at the locally based chain Finish Line include NCAA-licensed T-shirts for $7.99 and Nike and Under Armour fleece for up to 40 percent off. HHGregg, also based in Indianapolis, is offering an extra 10 percent off with a only a handful of exclusions. Both are offering free shipping.

Amazon.com, which started its Cyber Monday deals at midnight, is offering as much as 60 percent off a Panasonic VIERA 55-inch TV that's usually priced higher than $1,000. Sears is offering $430 off a Maytag washer and dryer, each on sale for $399.

How well retailers fare on Cyber Monday will offer insight into Americans' evolving shopping habits during the holiday shopping season. With the growth in high-speed Internet access and the wide use of smartphones and tablets, people are relying less on their work computers to shop than they did when Shop.org, the digital division of trade group The National Retail Federation, introduced the term "Cyber Monday."

"People years ago didn't have ... connectivity to shop online at their homes. So when they went back to work after Thanksgiving they'd shop on the Monday after," said Vicki Cantrell, executive director of Shop.org. "Now they don't need the work computer to be able to do that."

As a result, the period between Thanksgiving and Cyber Monday has become busy for online shopping as well. Indeed, online sales on Thanksgiving Day, traditionally not a popular day for online shopping, rose 32 percent over last year, to $633 million, according to comScore.

And online sales on Black Friday were up 26 percent from the same day last year, to $1.042 billion. It was the first time online sales on Black Friday surpassed $1 billion.

For the holiday season-to-date, comScore found that $13.7 billion has been spent online, marking a 16-percent increase over last year. The research firm predicts that online sales will surpass 10 percent of total retail spending this holiday season. The National Retail Federation estimates that overall retail sales in November and December will be up 4.1 percent this year, to $586.1 billion.

Retailer-specific numbers won't be available for a few weeks, but traffic was heavy on Friday at Finish Line's store at Castleton Square Mall, which opened at 7 a.m. Popular offerings included footwear door-busters up to 70 percent off, and college-licensed fleece, including Indiana University, Purdue, Ball State, UIndy, IUPUI and ISU, priced at two for $35.

HHGregg opened at 10 p.m. Thanksgiving day, with specials including a 73-inch HDTV for $799.99, and a stainless-steel French door refrigerator for $888.88, both half off the regular price.

As other days become popular for online shopping, Cyber Monday may lose some of its cache.

Cyber Monday hasn't always been the biggest online shopping day. In fact, up until three years ago, that title was historically earned by the last day shoppers could order items with standard shipping rates and get them delivered before Christmas.

Even though Cyber Monday is expected to be the biggest shopping day this year, industry watchers say it could just be a matter of time before other days take that ranking.

"Of all the benchmark spending days, Thanksgiving is growing at the fastest rate, up 128 percent over the last five years," said Andrew Lipsman, a spokesman with comScore.

All told, a record 247 million shoppers visited stores and websites over the four-day weekend starting on Thanksgiving, up 9.2 percent over last year, according to a survey of 4,000 shoppers that was conducted by research firm BIGinsight for the National Retail Federation. Americans spent more too: The average holiday shopper spent $423 over the entire weekend, up from $398. Total spending over the four-day weekend totaled $59.1 billion, up 12.8 percent from 2011.

Retailers, which can make up to 40 percent of their annual revenue in November and December, were hoping Thanksgiving openings and other incentives would help boost what's expected to be a difficult holiday shopping season.

The National Retail Federation estimates that overall sales in November and December will rise 4.1 percent this year, to $586.1 billion.

That's more than a percentage point lower than the growth in each of the past two years, and the smallest increase since 2009, when sales were nearly flat. Matthew Shay, president and CEO of the National Retail Federation, said retailers can be encouraged by the first weekend of the holiday shopping season.

"Retailers and consumers both won this weekend, especially on Thanksgiving," he said.