Amazon.com Inc took a big gamble this year by expanding its annual Prime Day summer sale to four days from two, betting the extension would give shoppers more time to navigate the millions of deals on its sprawling web store.

Retail analysts say the first day of Amazon’s Prime Day event and competing sales drove solid online spending.

U.S. online sales jumped 9.9% year over year to $7.9 billion on Tuesday, the kickoff of Amazon’s Prime Day megasale, according to Adobe Analytics