Cyber Monday sales were on course to bring in a record $9.4 billion, according to early estimates, building on a bumper Black Friday weekend for US retailers driven by earlier-than-usual promotions and free shipping.
Shoppers have already had nearly a month of special offers and deals as retailers look to draw out their vital holiday season, which is 6 days shorter this year due to a late Thanksgiving.
Estimates from Adobe Analytics on Monday predicted that some $72.1 billion has been spent online in the past month, with Cyber Monday - now traditionally the US economy's biggest internet shopping day - logging $473 million as of 10 p.m. (Manila time).
Amazon.com Inc and other traditional retailers such as Target Corp and Walmart have beefed up delivery services to fulfill online orders more quickly as more customers shop on their mobile phones and computers at home.
"At the end of the day, Cyber Monday is just Black Friday revisited so the momentum, and the deals, really started last week," said Carol Spieckerman, president at consultancy Spieckerman Retail.
"Retailers' click and collect capabilities are running more efficiently, online shopping is more intuitive... Amazon isn't the only one wearing the convenience crown this year."
It may not all be smooth sailing for the world's biggest online retailer. Protesters, who have described poor treatment of workers at its warehouses and rising climate emissions from the company's push for speedier deliveries, marched outside company chief Jeff Bezos' Fifth Avenue penthouse in New York City on Monday. "We're humans, not robots," read one sign.
Amazon did not immediately respond to a request for comment. The company aims to be carbon neutral by 2040, although its use of planes is on the rise.
Activists also staged protests across France on Friday and tried to blockade a shopping mall in Paris, denouncing the spread of Black Friday to European shores.
Target and Walmart have also taken aim at Amazon by making free shipping or same-day in-store pickups widely available.
The National Retail Federation estimates nearly 69 million Americans will scour the web on Monday for deals on everything from mobile phones to kitchenware, with Adobe estimating the biggest discounts on televisions and computers.
Topping Adobe's list of most popular products were Frozen 2 and Paw Patrol toys, L.O.L surprise dolls and Nintendo's Switch mobile console.
"#CyberMonday2019 The day of the year 85% of the US population pretends to actually be working," tweeted Erika Mayor, a user in Miami.