On an average, smartphone shoppers spent $102.02 per order, well below the $128 spent by desktop users.

Even though there was a big increase in usage and purchases, conversion rates were "depressing," said Scot Wingo, executive chairman of ChannelAdvisor.

Only 2.19 percent of visits to websites resulted in a sale, compared with 2.18 percent last year.

"The fact that we haven't improved the mobile conversion rate is a little depressing to be honest," Wingo said.

Cyber Monday refers to the Monday after Thanksgiving during which shoppers return to work, where many have high-speed connections.

As the tradition of Cyber Monday has grown over the last decade, online retailers have offered bigger promotions. The average discount on items sold during Cyber Monday was 21.5 percent, Adobe said in its report.

Among many strong performers, Amazon.com Inc stood out, clocking a 21.1 percent rise in Cyber Monday sales, according to e-commerce software provider ChannelAdvisor.

Discounts on Amazon.com averaged 40 percent, e-commerce analytics company Clavis Insight said.

Online sales were in stark contrast to the performance of brick-and-mortar retailers over the four-day weekend. Sales fell 10.4 percent from a year earlier to $20.43 billion, according to research firm ShopperTrak.