Supervalu Wednesday posted its weakest quarterly sales performance since Sam Duncan took charge of the supermarket company almost three years ago.

Third-quarter sales for all three of Supervalu's divisions were down from the same period a year ago, most notably for its discount Save-A-Lot chain, which Supervalu is looking to spin off. However, the company met Wall Street's profit estimates for the quarter.

Still, investors blanched: Supervalu's stock dropped 15 percent, or 93 cents, to close Wednesday at $5.08, hitting a low not seen since April 2013.

In a conference call with stock analysts, Duncan blamed part of Supervalu's third-quarter sales drop on forces beyond the company's control, namely deflation in meat prices, which is hurting Save-A-Lot. But he acknowledged that fewer customer trips to its conventional grocery stores — like Cub Foods in the Twin Cities — also played a role.

"Improving sales is a primary focus as we look to complete the fiscal year," Duncan said in a press statement.

Duncan, a veteran retail executive, took over as Supervalu's CEO in February 2013, less than a month after the troubled company announced the sale of its biggest supermarket chains.

Its stock was then trading near a 30-year low. Duncan, who plans to retire next month, began engineering a turnaround and Supervalu's stock rose until it topped $11 in April 2015. But, for the most part, it's fallen steadily since then and the turnaround seems to have stalled.

"We believe some challenges are priced in [to Supervalu's stock] at this point, but we do not expect an imminent turn in shares until we see definitive signs of top-line improvement," Rupesh Parikh, an analyst at Oppenheimer & Co., wrote in a research note Wednesday.

Eden Prairie-based Supervalu said Wednesday it earned $35 million, or 13 cents a share, in its fiscal third quarter ended Dec. 5. Adjusting for one-time charges, Supervalu earned $46 million, or 16 cents a share. That's in line with estimates from analysts polled by Thomson Reuters but down from 18 cents a share a year ago.

Sales were $4.11 billion, short of analysts' estimates of $4.17 billion and down 2.6 percent from a year ago, the biggest quarterly decline since at least 2013.

Supervalu's wholesale grocery business, its largest segment accounting for about half of revenue, recorded sales of $1.9 billion, down 3.5 percent from a year ago. The main culprit: One of Supervalu's customers, Albertsons LLC, transitioned its southeastern U.S. supermarkets to self-distribution, Bruce Besanko, Supervalu's chief operating officer, told stock analysts in a conference call.

At Save-A-Lot, same-store sales were down 3.4 percent over a year ago, the national chain's worst performance in several quarters. Same-store sales are a key gauge that takes into account recently opened and closed stores.

Stock analysts were expecting a decline, given Supervalu's issues in recent months with deflation in meat prices at Save-A-Lot. Meat is a prime item at the stripped-down Save-A-Lot, and falling meat prices have led to declining sales. "These levels of deflation were meaningfully greater than we had anticipated," Duncan told analysts.

Save-A-Lot, which accounts for about 25 percent of Supervalu's sales, is regarded by analysts as the company's crown jewel. Supervalu last week detailed plans to spin off Save-A-Lot into a separate publicly traded firm. On Wednesday, Duncan told analysts that any spinoff wouldn't be completed until the first half of 2017.

At Supervalu's conventional grocery chains, which include Cub, same-store sales fell 2.6 percent over a year ago. Conventional chains make up about 25 percent of Supervalu's business.

The company's conventional supermarkets were hurt by falling profit margins at its in-store pharmacies, To make up for that shortfall, Supervalu curtailed some store level promotions, which then hurt customer traffic, Besanko said.

Customer counts at Supervalu's conventional markets were down 4.3 percent during the quarter.

"Our real challenge comes down to traffic levels, which we readily acknowledge must improve," Duncan told stock analysts.