More shoppers grabbed doorbusters without heading out their doors on Black Friday, as millions opted to shop online.

Online sales for Black Friday leaped 21.5 percent over last year, according to IBM’s Watson Trend Hub, which analyzes online sessions and transactions on retail websites.

The online spike likely accounted for sparser crowds at malls. Sales at retail stores fell 10 percent to $10.4 billion this year, down from $11.6 billion in 2014, according to research firm ShopperTrak.