Although it was a Tuesday in July, many small businesses felt like they experienced Black Friday yesterday, courtesy of  Amazon.

Twice as many businesses took part in Prime Day, the online retailer's members-only sales event, compared with last year. And with twice as many deals available to customers, companies almost tripled the 14 million products sold during the inaugural Prime Day in 2015, according to Amazon. (The company declined to say how many small businesses participated in Prime Day this year.)

For consumer accessories company Sharkk, whose Bluetooth stereo speaker set sold out in less than an hour last year, taking part in Prime Day again was a no-brainer.

"This is one of the slower months in retail for everybody," founder Dov Brafman tells Inc. "And to have a day like this when you're doing in one day more than what you're doing on an average month in revenue is tremendous." Prime Day was Sharkk's biggest sales day ever, and brought in three times the revenue of Black Friday last year, Brafman adds.

Fashion-forward headphones startup LSTN, which said it doesn't typically offer any discounts, sold its products for up to half off on Amazon Tuesday. Founder and CEO Bridget Hilton also says it was her company's biggest sales day of the year. And Petcube, which makes a Wi-Fi camera for monitoring pets, had a waitlist for its product starting early in the day.

Slyde Handboards?, a company that appeared on Shark Tank and whose products are now part of Mark Cuban's Amazon Exclusives collection, offered more than 20 percent off on its unique surfboards. The company's sales were around six times what it makes in a typical day on Amazon, says Slyde co-founder Angela Watts. 

"We actually sold more units [during Prime Day] on Amazon than we did the night we aired on Shark Tank," she adds.

Behind the scenes of Prime Day

To participate in Prime Day, businesses had to offer discounts of at least 20 percent and provide $5,000 worth of inventory, according to Brafman. Amazon handled the majority of Prime Day marketing, but Sharkk made moves to ensure its products stood out among the 100,000 deals on offer. The company offered 30 to 50 percent discounts for higher valued items, earning them "premium placement" on the site. "We could have made a little more money by making a smaller discount but we focused on feeding on what Amazon wants, what the Amazon customers want to see," Brafman says. "Because of the quality of our deals, Amazon really pushed them for us."

For Slyde Handboards, getting ready for Prime Day meant handling the logistics of shipping out about four times the amount of inventory it usually keeps in Amazon's fulfillment centers. As is the case for most small businesses, committing on large amounts of inventory is a big gamble that can strain cash flow--but one that paid off on Prime Day. A bit of marketing strategy also helped the cause: Slyde combined email lists with three other Mark Cuban-sponsored companies participating in Prime Day deals to reach out to more than 80,000 people.

Other large retailers, including Walmart, Target, and JCPenney, made a push to jump on the Black Friday-in-July bandwagon. But for small businesses, "There's no bigger sales engine than Amazon," says Tom Caporaso, CEO of e-commerce solutions company Clarus Commerce. "You're literally going to get millions of shoppers exposed to your brand or your product, and that's something [you] probably couldn't afford doing the regular advertising channels."

Now that Prime Day has passed, however, Caporaso says the real challenge begins for small businesses that profited from the event: "How do you engage that shopper or consumer for the long haul?"