In the Southern California town of Beaumont, Walmart shoppers must first drive past the new Aldi, a recent addition to the family-owned German grocery-store chain that is beating the U.S. retail giant at its own game: selling food at rock-bottom prices.

Aldi is betting that many in Beaumont will never make it to the Walmart. Like hundreds of other stores Aldi has opened in recent years, the Beaumont store is strategically situated to siphon off the retail giant’s discount-seeking shoppers with prices that can average almost 20 percent less than those at Wal-Mart Stores.

Aldi stores lack the massive size and selection of a Walmart — they tend to be about one-tenth the size of an average Walmart and carry few national brands. Yet their rapid proliferation and the chain’s ability to offer even lower prices than those at Walmarts are putting pressure on the Bentonville, Ark.-based discounter. And as Aldi expands aggressively in the United States, it’s becoming just the latest in a long list of problems for Wal-Mart.

“It’s like a thousand cuts,” said Leon Nicholas, a senior vice president at consulting firm Kantar Retail. “They are impacted by Aldi, by Amazon, by the dollar stores — and all these things add up for Wal-Mart.”