Cyber Monday 2017 is going down in the history books.

Digital transactions on Monday reached a record $6.59 billion, Adobe Insights unveiled Tuesday in its final update on the holiday weekend. That marks a 16.8 percent increase from a year ago and makes Monday the largest online shopping day in U.S. history.

Mobile also had a record day, Adobe found, saying smartphones have become the “de facto device” for on-the-go shopping. Mobile sales on Cyber Monday reached $2 billion for the first time.

“This year, mobile shopping was dominant both in the morning and afternoon, and desktop only staged a comeback in the evening when people were home,” said Taylor Schreiner, director of Adobe’s Digital Insights division.

Adobe measures 80 percent of online transactions from 100 major U.S. retailers.

From Nov. 1 through Nov. 27, $50 billion has been spent online thus far, on track to reach $100 billion by the New Year, the firm said Tuesday.

A record $5.03 billion was spent online during Black Friday, an increase of 17 percent when compared with last year, Adobe found. Top-selling items that day included the Nintendo Switch, Hatchimals, L.O.L. Surprise and ride-on cars for kids.

Meanwhile, Small Business Saturday and Sunday delivered a combined $5.12 billion in online sales, up 10 percent from a year ago, according to Adobe.

“People are really figuring out how to use their mobile devices,” Mickey Mericle, vice president of Adobe’s Marketing and Insights division, told CNBC’s “Squawk Alley” Monday afternoon.

“And retailers are figuring out how to optimize … for mobile,” she added. “We’re seeing the two come together.”

Internet giant Amazon looks to be the biggest winner in this year’s surge in online retail sales, as 2017 comes to a close.

Companies including Wal-Mart, Target, Kohl’s and Best Buy are pushing offers online earlier and for a longer duration of time, yet analysts say Amazon will capture up to 50 percent of total e-commerce holiday sales.

Looking back on the year, Amazon has made strides in the fashion department, building out its private-label lines and luring top brands such as Nike and Calvin Klein to its platform.

In purchasing Whole Foods, Amazon drastically expanded its fresh food assortment. And the company is also making moves, albeit quietly, in the pharmaceuticals industry.

On Monday, Amazon said it sold “millions” of Alexa-enabled devices, as the company continues to grow its network of paying Prime subscribers.

GBH Insights analyst Daniel Ives has predicted Prime customers will spend up to 25 percent more on Amazon.com, when compared with a year ago.