Dive Brief:

• Cyber Monday sales reached a record $3.45 billion, a 12.1% growth over the year-ago period, according to an Adobe Digital Insights report on Tuesday. Sales surged past Adobe's forecast of $3.36 billion.

• Mobile, the big winner of Black Friday sales, generated 53% of online visits and 35% of sales, as of Monday evening.

• Best-selling electronics included Sony PlayStation 4, Microsoft Xbox, Samsung 4K TVs, Apple iPads and Amazon Fire; while the best-selling toys were Lego sets, Shopkins, Nerf, Barbie and Little Live Pets.

Dive Insight:

Cyber Monday is out, and Cyber Week is in.

Traditionally, Black Friday has always won in-store sales while Cyber Monday has held the edge on digital dollars, but this year, the race is tight. Cyber Monday sales are predicted to just barely overtake Black Friday’s record-breaking online sales of $3.34 billion.

"Cyber Monday is on track to hit our prediction of $3.36 billion and could retain its position as the top online shopping day of the season, but only if retailers continue to push as good of deals today as they have over the holiday weekend," Becky Tasker, managing analyst for Adobe Digital Insights, said in a statement supplied to CNBC.

Cyber Monday itself is certainly becoming less exclusive, given that this year consumers have already had several days to peruse the same online deals. For the first time, Wal-Mart kicked off its Cyber Monday deals on Friday at midnight, whereas last year the retail giant waited until Sunday to roll out its digital deals. Amazon also unveiled deals for the week of Cyber Monday on Friday, touting 75,000 promotions, and Macy’s and Target promoted “Cyber Week” as opposed to “Cyber Monday,” but waited until Sunday to roll out their bigger digital promotions. In all, Retailers are featuring 4% fewer deals on Cyber Monday than on Black Friday, according to e-commerce analytics company Clavis Insight.

Most retailers are keeping data under wraps until the end of the day, but JC Penney this morning tweeted that toys were "driving strong traffic online and has quickly become one of the highest searched terms on JCPenney.com." By early afternoon, Target announced its five best deals from Sunday (the start of its Cyber Week): PlayStation, Xbox and Nintendo Wii U gaming systems, KitchenAid mixers, the Apple Watch, Nest thermostats and the Star Shower Motion Laser Light projector.

Early reports showed no indication of noticeable website service outages on Monday (which last year plagued Target's website), and Macy’s seems to have recovered from the site disruptions it experienced on Black Friday.

"There’s a lot at stake this holiday season,” David Jones, director of sales engineering and APM evangelism for Dynatrace, said in a note emailed to Retail Dive. “Since even a half-second increase in site speed can impact conversions by 11%, retailers need to be sure their websites and mobile apps don’t buckle under the pressure of peak online holiday shopping.”

As the holiday weekend comes to end and consumers go back to work, retailers are hoping to reel in the last of the deal seekers, but some consumers are saying enough is enough: Many took to Twitter to rant about the barrage of emails from sale-hungry retailers, Time's Money.com reported.

Deleting #CyberMonday emails like pic.twitter.com/K0AsHiLiav

— Kelly Schumacher (@kdschumacher) November 28, 2016

Sam Cinquegrani, CEO of ObjectWave, a digital marketing technology and services company, predicts retailers who put significant work into their online systems should stand out as clear winners of Cyber Monday, predicting Target and Macy’s as well as specialized retailers such as Sephora and Home Depot will come out on top.

“Retailers have gotten smarter operationally — so while you won’t see much difference in functionality, we are seeing retailers package goods together, fix a sale more appropriately and effectively,” Cinquegrani said. “For example, Amazon is doing efficiency pricing with packaging — putting more items in a box, etc. And they’re also doing same-day delivery, utilizing logistics teams in certain markets. In-store pickup is on the rise, too.”

The blockbuster weekend bodes well for the holiday season: Online shopping has accounted for $36.5 billion in online revenue so far this holiday season, Adobe reports, with 26 out of 27 days in November generating $1 billion each day.

This story is part of our ongoing coverage of the 2016 holiday shopping season. You can browse our holiday page for more stories.