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Online shoppers in the U.S. made $1.2 billion of purchases via their phones and tablets on Black Friday, marking the first billion-dollar mobile shopping day in U.S. history, according to estimates from Adobe. The estimate marks a 33 percent increase over last year’s mobile sales total for the day.

Overall, Adobe predicts that total online sales reached $3.34 billion on the huge discount shopping day, on which retailers are increasingly running the same discounts online as they do in their stores.

Large retailers that have invested heavily in their mobile websites and apps are seeing big gains this holiday season. At Fanatics, an online retailer of licensed team sports apparel, 56 percent of Thanksgiving Day sales happened on mobile — 42 percent via phones and 14 percent via tablets. These numbers were likely helped by consumers making purchases while watching the day’s slate of football games.

American consumers are increasingly comfortable making purchases via their phones, and the popularity of larger screen sizes is one contributor. Payment methods that simplify the checkout experience — think Apple Pay, Android Pay and PayPal One Touch — are starting to help, too.

Still, when it comes to mobile commerce, the U.S. lags way behind some international markets such as China. On Singles Day, China’s biggest shopping day, mobile commerce accounted for more than 80 percent of sales on Alibaba’s shopping sites.

Watch: Why Is Black Friday Still a Thing?