Amazon’s third annual Prime Day has come and gone. This year's event now ranks as the biggest sales day ever in Amazon history, surpassing both Black Friday and Cyber Monday, according to an Amazon statement emailed to Retail Dive.

Prime Day 2017 — which lasted 30 hours this year compared to 24 hours for the two previous events — grew by more than 60% compared to the same 30 hours last year, and sales growth by small businesses and entrepreneurs was even higher, Amazon said. 

The Echo Dot was a big winner this year. The portable Alexa-enabled speaker was not only the best-selling Amazon device, but also the best-selling product from any manufacturer in any category across Amazon globally, according to the company. Prime members purchased seven times more Amazon Echo devices globally during this year's event than on Prime Day 2016. 

But Amazon really hit the mother lode in growing its Prime membership program as more shoppers joined to access deals. More new members joined Prime on July 11 than on any previous day in Amazon history. “Tens of millions of Prime members made a purchase on Prime Day 2017, more than 50% higher than the prior year,” the company said in a statement.

"Amazon is defying the traditional laws of retail physics which dictate that growth slows after a retailer reaches 25% market share. This demonstrates how different Amazon is from any other retail entity," Matt Sargent, senior vice president of retail at Frank N. Magid Associates, told Retail Dive in an email. "The ability of Prime to build aggressively upon its base (42% of US consumers) demonstrates that Amazon is succeeding in its strategy to build an ecosystem that is undeniably attractive to all customers."

The day before Prime Day, Retail Dive listed nine reasons why Prime Day matters — to Amazon and the rest of retail. Today, we break down the five biggest takeaways from this increasingly significant event in retail. 

1. Prime Day 2017 had fewer fails

There were similar criticisms as in years past — #PrimeDayFail made its return on social media — but overall, the event ran rather smoothly. Amazon, it seems, is learning from its mistakes. 

“Between the cross-channel marketing activity leading up to Prime Day, and the structure and categorization of the deals themselves on Prime Day, it is clear Amazon strategized to make the shopping experience easier for consumers to navigate this year,” Ryne Misso, director of marketing for Market Track, told Retail Dive in an email. “This is likely a reaction to much of the consumer feedback seen across social media channels after the first two Prime Days, which criticized the event for not offering deals on popular categories and products.”

2. Targeted deals grew key categories, but grocery lagged

On Prime Day, Amazon was strategic in its selection of products and categories to feature, and grouped them by “most-shopped themes,” such as items for pet lovers, gardeners and kids. The most popular themes on Prime Day were those for home Chefs, techies and “for the home.”

Electronics, toys and even apparel were called out in Amazon’s press release Wednesday morning. Amazon tends to create bulleted lists of specific best-selling items to illustrate the vast volume of goods moved in any given event.

On Prime Day 2017, “more than 3.5 million toys were purchased” and “more than 200,000 women’s dresses and more than 200,000 lightbulbs were purchased by customers,” among many others. But while Amazon strategically offered deals in the grocery category, the early results fail to mention much in the way of popular items purchased on Prime Day.

Not much was said about grocery — and that's worth noting. Grocery is a key category that Amazon is looking to grow, with the company's $13.7 billion acquisition of Whole Foods Market and other weapons — including proprietary technology — at its disposal.

“Nearly 70% of the Alexa-only Prime Day Deals were for CPG products, from candy to home consumables such as paper towels and toilet paper,” points out Misso. “It may indicate that Amazon has plans to leverage Alexa, and voice-activated commerce, in their efforts to gain more traction in the grocery space.”

Prime Day 2018 could be a different story once the Whole Foods acquisition is absorbed and synergies begin to click between Amazon and its brick-and-mortar grocery business.

3. Amazon killed the competition

Rival retailers rolled out sales of their own but Amazon still came out on top. “Amazon maintained a distinct competitive price advantage on Prime Day deals, even against retailers that attempted to match their price,” said Misso.

Walmart had the largest overlap in the number of items with Amazon by mid-day, although the majority of those were offered by third party marketplace sellers, according to Boomerang Commerce.

Target defended its core categories, particularly kids, with a 39% overlap in selection. But the retailer couldn’t beat Amazon on price — it was 44% more expensive in the kids assortment, according to Boomerang, while Walmart was 47% more expensive. Both Walmart and Jet matched Amazon’s price on several Prime Day Deals, said Misso, but in the aggregate, Amazon bested them all, particularly in these key categories.

Electronics was the most popular category on Prime Day 2017 — just as in years past — and electronics retailer Best Buy clearly planned accordingly. Best Buy was the best at matching assortment in the tech category with a 48% overlap and having the most competitive pricing at just 27% more expensive, according to Boomerang.

Marketing technology company Amobee told Retail Dive in an email that between July 10 through 6 a.m. Eastern time on July 11, 2017, 39% of all Prime Day digital content engagement mentioned TVs, 30% of Prime Day digital content engagement brought up tablets, and 19% of all Prime Day digital content engagement was phone related — falling right into Best Buy’s prime market.

"Amazon maintained a distinct competitive price advantage on Prime Day deals, even against retailers that attempted to match their price,” said Misso. “In a price comparison on over 50 Prime Day Deals, Amazon was priced 15% lower than Walmart, 29% lower than Jet, and over 40% lower than Best Buy and Target, on average.”

Internet Retailer found that nearly half of the 100 largest online retailers were offering competing promotions on Prime Day.

4. Amazon won the marketplace battle

If Amazon and Walmart are engaged in a heated war to operate the largest online marketplace — and they most certainly are — Amazon won the battle on Prime Day 2017.

“Prime Day 2017 was another record-breaking success for small businesses and entrepreneurs worldwide who participated in the event,” the company said in a statement while sharing comments from participating sellers.

“Overall, for the Prime Day event (all 30 hours), we saw about 20 times more overall sales. This is a huge benefit to our business, as it gives us exposure to thousands of new customers, and helps us with cash flow as we ramp up on inventory for the Holiday Season,” said Ben Arneberg of Boston-based Willow & Everett.

“So far, this year’s Prime Day sales increased 350% from last year’s," said Marcia Ricchiuti of Kahili Creations in Pahoa, Hawaii. "Getting the opportunity to offer lightning deals as a Handmade at Amazon artisan has been a boom to my business.”

5. New members and Amazon products were the real Prime Day bonanza

Amazon employees were handing out bananas at two locations in Washington, D.C., popping up with an East Coast outlet of the company’s iconic Seattle banana stand. Perhaps it was to signify the bonanza Amazon was about to reap with sales of Amazon-branded products — the very devices that make it easier for shoppers to buy more products from Amazon, more often.

In 2016, only three of the 10 products most associated with Prime Day in digital content engagement were proprietary Amazon products, Amobee told Retail Dive. But by midday of the 2017 event, five of the 10 products most associated with Prime Day were Amazon-branded items

"Even as Prime Day has continued to expand in scope, Amazon has become more skilled in shifting the focus of the event on their own product lines," Jonathan Cohen, principal brand analyst at Amobee, told Retail Dive in an email. “The advantage for Amazon in concentrating their Prime Day efforts around selling proprietary hardware is the more unique data they have around their audience, the larger the competitive advantage they have in understanding how to sell even more products to that same audience. For other retail brands trying to compete with Amazon and their end to end digital ecosystem, it's not enough to just price match or run competing promotions during specifics events; the emphasis needs to be on findings ways to get a more holistic view of the digital audience and their interests." 

While Amazon claims "tens of millions" of Prime members and offered no firm numbers on how many more joined during the Prime Day 2017 event, many likely opted for the free 30-day trial membership. It's not clear how many will continues as paying members, but Prime has proven to be quite sticky, with most members staying on and spending significantly more than non-members.

"Once consumers try Prime, 73% become paid members. And after that first year, retention rates stay in the 90%-range," said Lindsay Bloom, senior marketing manager at SessionM, in an email to Retail Dive. "Prime Day started as a one-day anniversary sale — a common sales tactic deployed by many retailers. But it has grown into arguably the most successful loyalty campaign ever created."

Sales aside, the real benefit of Prime Day for Amazon has always been the ability to grow Prime and lock more shoppers into the program.

"The beautiful thing about Amazon’s approach with Prime Day is not just the acquisition of customers and subscription fees," said Bloom. "It is the way that Amazon uses its data to foster long term loyalty among its members."