Walmart Inc. is expanding next-day delivery for third-party marketplace orders to the nation’s largest metropolitan areas, including New York, Los Angeles, Chicago, Houston and Atlanta. The service, provided through Walmart Fulfillment Services, builds on the retailer’s effort to match the speed of rivals such as Amazon and will initially cover high-volume items sold by outside merchants on Walmart.com. The rollout was announced at the company’s Marketplace Seller Summit, where executives also introduced a suite of artificial-intelligence tools designed to make it easier for merchants to list products and manage inventory. Walmart said the new capabilities can cut fulfillment costs by about 15 % compared with competing services and have lifted gross merchandise value on “Walmart Fulfilled” products by roughly 50 %. E-commerce sales at Walmart rose 25 % in the most recent quarter, and the Bentonville-based retailer reiterated that it expects its U.S. digital business to turn a profit in the current fiscal year. To spur further growth during the peak holiday season, Walmart will temporarily waive or slash referral fees on select toys, pet supplies and other top-selling categories.