This is good news for consumers, but not so much for the electronics retailers who plan to engage in a dogfight for market share when it comes to selling smartphones, tablets, TV sets and other gadgets. Walmart said this morning that it will “match select Black Friday offers from Target, Toys R’ Us and Best Buy” beginning Friday — a week ahead of the traditional post-Thanksgiving sales. And Best Buy shares are down 10.6% so far today after it warned investors that its pricing plans will “have a negative impact” on profit margins in Q4. “We will not be shy about investing in winning the holiday season,” CEO Hubert Joly said. The warning “spooked investors,” says B. Riley analyst Scott Tilghman, who trimmed his Q4 forecasts for the chain. Retailers are antsy because Thanksgiving — celebrated the fourth Thursday in November — appears this year on the latest possible date. “With six fewer days from Thanksgiving to Christmas, the retail environment is more competitive than ever,” said Mac Naughton Duncan, Walmart’s U.S. Chief Merchandising and Marketing Officer. Walmart’s move follows Sears and Kmart’s announcement that they’ll begin their sales a week early. More than half of retailers will start their holiday promotions at least five days before Thanksgiving, the National Retail Federation said last week. Many stores also are cutting prices to compete with online retailers including Amazon. The retail trade group says its surveys show that about 140M people likely will go shopping over the four-day Thanksgiving weekend, down from 147 million who planned to do so last year.