The same-day delivery wars have been fully engaged in Los Angeles.

Google Inc. and Barnes & Noble Inc. last week launched a joint assault on mutual competitor, offering same-day delivery for titles purchased at two of the bookseller’s 13 L.A. stores.

Shoppers at the retailer’s stores in Marina del Rey and on the Third Street Promenade in Santa Monica will have access to Barnes & Noble’s inventory through Google Shopping Express, which already partners with such local retailers as Target and Costco to bring same-day deliveries to customers’ doorsteps.

Jaime Carey, Barnes & Noble’s chief merchandising officer, said the companies had been in discussions since March, when Google contacted the bookseller. Barnes & Noble expects local stores’ physical sales to increase as the service will reach people in Google’s consumer base who aren’t necessarily loyal Barnes & Noble customers.

“When you serve the customers that you have better, and you add to that a service that brings in new customers, we expect to amplify our business,” he said.

Amazon launched same-day delivery for certain retail partners last year in Los Angeles. It announced last week that it was expanding that delivery service to 10 cities from four.

Google started its express shipping service in San Francisco last year, but its new partnership with Barnes & Noble is its first strike at Amazon’s dominance in the book market – a dominance that has come largely at Barnes & Noble’s expense.

Barnes & Noble reported that its retail segment, which covers brick-and-mortar bookstores and, had net income of $354 million for the fiscal year ended May 3, down 6 percent from the same period a year earlier. Revenue for the bookseller’s retail business also fell 6 percent, to $4.3 billion.

For Google, the partnership with Barnes & Noble provides an opportunity to chip away at Amazon’s grip on the e-commerce market. Other cities testing the partnership with Barnes & Noble are New York and San Francisco.

Barnes & Noble will provide inventory; Google will process orders and handle shipping. A Google Shopping Express representative will also be available on site.

“Our regular customers should not worry as there will be no changes to our store as a result of this partnership,” said Frank Varela, the community business development manager at the Santa Monica location.

That store had been working with Google Shopping Express staff for a few weeks, according to one employee there, to prepare the store for last week’s launch.

Google plans to expand its Shopping Express program in the coming months to Beverly Hills, Pacific Palisades and West Hollywood.