Kemper Isely
Analyst · Wolfe Research
Thank you, Jessica, and good afternoon, everyone. Thank you for joining us today. We delivered another strong performance in the third quarter, exceeding our expectations. We saw sales trends improve sequentially, while continuing to face difficult year-over-year comparisons. Our focus on delivering the highest-quality natural and organic products at always affordable prices as well as being a resource for science-based nutritional education continues to drive high levels of engagement with our customers.
First, I would like to highlight a few key performance metrics from the third quarter. Daily average comparable store sales for the third quarter were down 3.6% against a 15.5% increase in the third quarter of last year. On a 2-year stacked basis, daily average comparable store sales accelerated to 11.9% in the third quarter, up from 10% in the second quarter. On our second quarter earnings call, we noted that the transaction count comp had turned positive in April. Transaction count comp remained positive through the balance of the third quarter, creating a new inflection point with transaction count comp up 4.1% for the quarter, while basket size comp was down 7.4% as customers began to return to pre-pandemic patterns.
The basket has remained elevated as compared to the pre-pandemic level, up over 20% compared to the third quarter of 2019. Operating income increased by 5.4% as compared to the third quarter of 2020, driven by lower store expenses and 40 basis points of gross margin expansion. And earnings per share of $0.22 was above our expectations and higher than the third quarter of last year. We were focused on several key initiatives in the third quarter, which contributed to our positive results.
During the quarter, we were excited to open relocated stores in the communities of Pueblo, Colorado and Midland, Texas. Opening new stores and relocating stores has been challenging this year due to delays we are experiencing in the construction process and equipment deliveries. We intend to return to opening between 6 and 8 new stores per year as these conditions improve.
The {N}power loyalty program remains an important tool for optimizing promotional activity and driving customer engagement. We ended the third quarter with over 1.4 million {N}power members, up 17% versus a year ago and up 4% sequentially. Our net sales penetration for {N}power was 71% in the third quarter compared to 68% a year ago and up slightly from the second quarter. During the third quarter, we continued to strengthen our portfolio of Natural Grocers brand products, a key point of differentiation versus our competitors. The relaunch of our private brand supplements that began in March grew in the third quarter to include a comprehensive range of over 115 vitamins, herbs, minerals and precision formulas.
Our branded supplements are made from high-quality ingredients, are good manufacturing practices certified and affordably priced. Additional branded supplements are under development, and we expect to have approximately 150 SKUs at the completion of the initial rollout. We plan to further expand the number of SKUs over the coming years. In addition to supplements, we added 14 new products to our brand assortment, including jarred olives and vegetables and liquid dish soap.
For the quarter, the sales penetration rate of our Natural Grocers brand products was 7.1%. We are also very excited to highlight our recent launch of GardenBox, which brings fresh, hydroponic, organic produce to the individual store location. We are piloting this program at our Green Mountain store in Lakewood, Colorado, starting with an assortment of lettuces priced at $1.99 per head. On the outside, the GardenBox looks like a regular shipping container. Inside, innovative technology controls every aspect of the growing process, including water, temperature, light and nutrients to optimize growth and nutrition.
One of our core values is supporting our communities and good4u crew. During the quarter, we launched our National Grocers Heroes in Aprons Fund. This fund is a 501(c)(3) charitable entity, providing financial assistance to both our crew who experienced unanticipated hardships, and direct grants to Natural Grocers' charity partners in the community. We are excited and proud to have established a fund to oversee our legacy of providing support to our crew and communities.
Finally, I would like to thank our good4u crew for their continued hard work and commitment. They are the key to delivering on our goals while staying true to our founding principles. With that, let me turn the call over to Todd to discuss our financial results and guidance.