Ali had Frazier. Coke has Pepsi. The Yankees have the Red Sox.

Now Wal-Mart, the mightiest retail giant in history, may have met its own worthy adversary: Amazon.com.

In what is emerging as one of the main story lines of the 2009 post-recession shopping season, the two heavyweight retailers are waging an online price war that is spreading through product areas like books, movies, toys and electronics.

The tussle began last month as a relatively trivial but highly public back-and-forth over which company had the lowest prices on the most anticipated new books and DVDs this fall. By last week, it had spread to select video game consoles, mobile phones, even to the humble Easy-Bake Oven, a 45-year-old toy from Hasbro that usually heats up small cakes, not tensions between billion-dollar corporations.

Last Wednesday, Wal-Mart dropped the price of the oven to $17, from $28, as part of its “Black Friday” deals. Later the same day, Amazon cut its price, which had also been $28, to $18.