U.S. retailers’ September same-store sales topped analysts’ estimates, led by discount and specialty-apparel chains that benefited from back-to-school shopping, while department stores trailed projections.

Costco Wholesale’s revenue at stores open at least a year rose 6 percent in September, beating Wall Street’s view.

Analysts surveyed by Thomson Reuters expected a 5.7 percent increase in the figure.

Revenue at stores open at least a year is a key gauge of a retailer’s health because it excludes results from stores recently opened or closed. Issaquah-based Costco said Thursday that the metric climbed 6 percent at its U.S. locations and increased 7 percent at wholesale clubs overseas.

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Stripping out the impact of higher gas prices and foreign-currency exchange rates, revenue at stores open at least a year rose 5 percent for the total company and for U.S. locations. The figure climbed 6 percent internationally.

Nordstrom said Thursday that sales in stores open at least one year rose 4.4 percent in September, slightly below analysts’ expectations.

The company said sales suffered in early September because returns increased due to the later start this year of the department-store chain’s big anniversary-sale event.

Seattle-based Nordstrom said it was also competing against strong figures from September 2011 — a 10.7 percent jump in same-store sales — when the company offered free shipping and free returns for online purchases.

Analysts predicted a gain of 5 percent in sales at locations open at least a year, according to Thomson Reuters. The figure is closely watched in retailing because it excludes new stores and those that closed.

The department-store chain said retail sales in the five weeks ended Sept. 29 rose 7.4 percent to $1.01 billion, compared with $943 million in the same period last year.

Sales at TJX climbed 6 percent, beating the average estimate for a 4.4 percent gain from analysts surveyed by researcher Retail Metrics. Target, the second-largest U.S. discounter, posted a 2.1 percent increase in same-store sales, topping the 2 percent projection.

“The winner of the group is TJX,” said Ron Friedman, head of retail and consumer products at accounting firm Marcum. “They’re where everyone was last year, but they’re still there, and nobody else is there really. They had the right product; they hit the kids for back to school.”

Same-store sales for the more than 20 companies tracked by research firm Retail Metrics rose 3.9 percent, excluding drugstores. That topped analysts’ average estimate of a 3.7 percent gain. Sales increased 5.9 percent in August. Specialty-apparel chains led the gains with a 5.6 percent increase, while discounters rose 4.3 percent and department-store sales increased 1.4 percent.

“It’s slow, steady, growth,” said Barbara Kahn, a marketing professor at the Wharton School of the University of Pennsylvania. “The retailers understand the market much better now, they plan inventories better now, they understand you have to do something interesting to bring people into the store.”

Macy’s, the second-largest U.S. department-store chain, reported a 2.5 percent increase, trailing analysts’ estimates for a 3.3 percent gain.

On Tuesday, Lynnwood-based specialty sports equipment and clothing company Zumiez reported revenue at stores open at least a year climbed 5.6 percent in September. Total revenue for the five weeks ended Sept. 29 rose 18.6 percent to $62.7 million.

For the quarter to date, revenue at stores open at least a year increased 4.6 percent.