For Wal-Mart Stores Inc. and Amazon.com Inc., the holiday shopping season is shaping up to be a battle between the Godzilla of retail and the King Kong of e-commerce.

The current price war over hot coming books is just the tip of the iceberg. In recent months, the two companies have increasingly copied each other's playbooks online and are treading more on each other's turf. Walmart.com Chief Executive Raul Vazquez said in an interview that Wal-Mart would continue targeting rivals such as Amazon with other hard discount promotions...