Walmart has always excelled at selling products in its cavernous stores. It appears to be getting its head around selling online, too.

On Thursday, the company said e-commerce sales had grown 63 percent in the United States in the latest quarter. The unexpected leap offered the strongest evidence yet that Walmart, the country’s largest retailer, is making headway in its effort to be as prominent online as it is across the American landscape.

“This is extraordinary growth, and we’re pleased with the traction we’re generating across our e-commerce offerings,” said Brett Biggs, Walmart’s executive vice president and chief financial officer.

Now the question is whether the company can sustain that growth to become a fiercer competitor to the online juggernaut Amazon. Walmart has invested heavily into building its online business over the years, but the results have been mixed — and Amazon has surged.