Online retailer Amazon.com yesterday defied the laws of retail gravity, posting a robust jump in fourth-quarter profit at a time when most peers are swooning or shutting down altogether.

The world’s largest Internet store reported an eye-popping 8.7 percent jump in fourth-quarter profit to $225 million, or 52 cents a share, up from $207 million, or 48 cents, a year earlier.

Amazon had bragged that the holiday-shopping season was its best ever, despite the nationwide collapse in consumer spending, and the sterling results proved true to that promise, solidifying its status as e-commerce leader among analysts and investors.

* The news is particularly gratifying for Amazon chief Jeff Bezos, considering that online auctioneer eBay last week reported its fourth-quarter net income plunged 31 percent.

Amazon.com shares rose 14 percent in after-hours trading to $56.65, up from its closing price of $50 a share.

The company bucked the trend of slumping sales amid job cuts and falling home prices by slashing prices, providing free shipping and vastly expanding its product line, analysts said.

When Amazon went public in 1997 it was known primarily as an online bookseller. Today, the company sells everything from shoes to musical instruments.

Bezos also noted strong sales of the company’s electronic reader, the Kindle. Bezos declined to disclose the number of units sold, but the company said it was the second year in a row that it sold out ahead of the holiday season.

Amazon expects first-quarter sales to rise between 9 percent and 19 percent, or up to almost $5 billion.