Online purchases reached $1.93 billion on Friday itself, the unofficial start of the retail sector's holiday season.
That marked a 39 percent increase over 2012, according to software maker Adobe, which analyzed 400 million visits on some 2,000 American shopping websites.
Technology giant IBM also found similar numbers for overall online sales as it looked at 800 merchant websites.
It said online sales jumped 19.7 percent on Thanksgiving and 19 percent on Black Friday, with orders averaging $135.27, a 2.2 percent increase compared to last year.
Online shoppers may have been wise to avoid stores, with reports of fistfights, a stabbing and a shooting as people elbowed their way through crowded shopping floors to snatch heavily discounted items.
Sales from mobile devices accounted for 24.2 percent of the total, according to Adobe, with purchases from tablets representing 15.6 percent of those sales and purchases from smartphones representing 8.6 percent.
Similarly IBM found that mobile devices accounted for 21.8 percent of sales.
According to Adobe, of the $3 billion in total online sales over the two days, $417 million was done on iPads and $126 million was done on iPhones, while Android phones were used to buy $106 million in purchases and Android tablets accounted for $42 million.
IBM said tablets were used for 14.4 percent of online sales, against 7.2 percent on smartphones. On average, tablet users each spent $132.75 and smartphone users spent $115.63.
The company also found that iPad and iPhone users spent more, shelling out an average of $127.92, compared to $105.20 for users of Google's Android system.
Adobe agreed that Apple users spent more than people using Android devices.
Purchases made from Apple devices accounted for 18.1 percent of total online sales, against 3.5 percent for Android devices.