Cyber Monday spending was expected to hit a record $3 billion, making it the biggest e-commerce day ever in the U.S. and a new peak after retailers on Thanksgiving and Black Friday saw more people buy things online than in stores.

The weekend shopping spree marked another step in the evolution of retail, with stores offering the same deals online as in stores and shoppers moving deftly between them.

"It is clear that the age-old holiday tradition of heading out to stores with family and friends is now equally matched in the new tradition of looking online for holiday savings opportunities," said Matthew Shay, president of the National Retail Federation.

The trade group said its research found that 34.6 million people shopped in stores on Thanksgiving while 41 million shopped online. On Black Friday, 74.2 million went into stores while 75.3 million shopped online.

The burst of online traffic overwhelmed Target Corp.'s website on Monday morning. Its online customers were placed in holding queues starting about 9 a.m. The issues were resolved by 10:30 a.m. Some difficulties with its mobile apps persisted through the afternoon.

Target attracted online shoppers with a 15 percent discount on all items, the first time it offered a sitewide promotion, and coupled the offer with free shipping. By noon, the order volume on the site was already twice as high as its previous busiest day, Target spokeswoman Jamie Bastian said.

The company had experienced traffic overloads and site crashes on days when it offered limited release of designer collections from Missoni and Lilly Pulitzer. Earlier this year, the company increased its mobile app's capacity sevenfold to handle growing demand.

Online sales account for about 3 percent of Target's $73 billion in annual sales.

Also Monday, some Internet users noted problems with the online payment company PayPal.

Several other retailers, including Victoria's Secret and Neiman Marcus, experienced outages with their websites or apps on Thanksgiving and Black Friday.

Consumers' growing use of online ordering, along with the spreading out of holiday shopping deals, led to thinner crowds in the nation's malls and stores over Thanksgiving weekend. Many retailers began promoting pre-Black Friday specials in early November. And Cyber Monday now extends into Cyber Week specials at many retailers.

While the number of people who placed online orders on Thanksgiving and Black Friday eclipsed the number of visitors to stores, people continue to spend less online than in stores.

Overall holiday spending is expected to increase about 4 percent this season.