NEW YORK (CNN/Money) - Online retailing got an early Christmas present this year as last-minute shoppers rewarded e-tailers with a huge jump in sales last week, a market research firm reported.

Consumers spent $2.45 billion online between Dec. 13 and Dec. 19, an increase of 57 percent from a year earlier, according to the latest figures from ComScore Networks.

As a result, online holiday sales are up 28 percent so far this year and are expected to cross $15.5 billion for November and December for the holiday shopping period, the report said late Wednesday.

"Retailers have worked tirelessly to translate the lessons of years past into improved merchandising systems and strategies, and the work is paying dividends this season," Dan Hess, senior vice president of ComScore Networks, said in a statement.

"Following a roller coaster growth pattern from one week to the next, the impressive last results we're seeing may bring the final tally over the top-end of our forecast," he added.

The report said a shift in the calendar is partially responsible for the late-season sales acceleration, as consumers got two extra shopping days this year between Thanksgiving and Christmas. Additionally, more retailers were offering discounted or free shipping incentives later in the season than in the past.

The "iPod" was among the most searched item on the Internet last week, with more than 1.67 million consumers looking up the product, a 150 percent jump compared to the previous week, the report said.