The supply-chain bottlenecks that have hobbled big retailers are proving to be a boon for off-price apparel sellers.

Executives at discount stores, including Burlington Stores Inc. and Ross Stores Inc., say their buyers have been snapping up late-arriving clothing and other goods as their full-price counterparts cope with backlogs at congested U.S. ports.

Ross Stores has been “able to capitalize on the volatility in the supply chain,” including stocks of apparel held for specific selling seasons, said Ross Stores Chief Executive Barbara Rentler during the company’s March 1 earnings call.

“We see more potential opportunities in front of us from closeouts,” Ms. Rentler said. “There’s a lot of that merchandise that vendors are still moving [that] is not necessarily even in the country.”