Why 4% growth is the secret ingredient for Wal-Mart beating Amazon

Amazon (AMZN)'s North American business has a $55 billion lead over Wal-Mart (WMT) online in the U.S. — and the world's largest retailer is unlikely to catch up, Moody's says.

Yet even as Amazon continues to record double-digit product sales gains, investors shouldn't get hung up on the companies' comparative digital growth rates, analyst Charlie O'Shea said. That's because Wal-Mart has one crucial advantage over Amazon: physical stores.

By leveraging its massive fleet, sales at Wal-Mart's U.S. locations only need to increase 4 percent to match a comparable period of 20 percent growth from Amazon North America, O'Shea said. In the latest quarter, Wal-Mart's U.S. sales increased 3.1 percent.

"Let's keep this in context," O'Shea said. "The brick-and-mortar guys have two businesses."

In the end, what matters are the actual dollar gains, O'Shea said. Though Wal-Mart's online sales growth has slowed in recent quarters , increasing roughly 12 percent in the second quarter, that still equates to nearly $2 billion in additional sales, according to Moody's estimates.

As traditional retailers search for ways to compete against Amazon, Wal-Mart is one of the companies forging ahead of its bricks-and-mortar rivals, Moody's says. Wal-Mart's $3.3 billion acquisition of Jet.com should continue to propel its digital revenues.

Moody's estimates Wal-Mart's domestic online sales were roughly $15 billion during the 12 months ended June. The firm expects that figure to grow to $35 billion in 2022.

While that pales in comparison to the $212 billion expected from Amazon's North American product sales that year, Wal-Mart is expected to maintain its lead in overall revenues. Though the gap between the two companies will narrow, O'Shea predicts Wal-Mart's 2022 domestic sales will still be far ahead of Amazon, at $464.4 billion to $399 billion.

"They're (Amazon) competing with people that have not only online businesses that are growing pretty rapidly, but also have these bricks-and-mortar businesses that aren't going to go away," he said.

Amazon has responded by testing the waters with physical stores, including more than a dozen pop-up locations from California to New York.

In addition to Wal-Mart, Moody's says Best Buy (BBY) is gaining ground online. The company, once thought to be an inevitable victim of Amazon, grew its U.S. digital sales nearly 24 percent during the second quarter .

Overall, Moody's projects online revenues will account for 20 percent of all retail sales in seven years. That compares with approximately 9 percent penetration today.