The market tracking firm reviewed price comparisons between many of the major retailers — Target, Best Buy, Wal-Mart and its Jet.com — throughout the day, finding that Wal-Mart's efforts to stay competitive clearly stood out from the rest.
Both Wal-Mart's website and Jet.com were "the closest in terms of price parity" on Prime Day, matching more of Amazon's deals than other retailers, Market Track said.
Still, Wal-Mart and Jet.com didn't come close to matching all discounted prices, Market Track added, and in some instances the firm found prices significantly higher on Wal-Mart.com than on Amazon.com.
Representatives from Amazon and Wal-Mart did not immediately respond to CNBC's request for comment on this data.
Source: Market Track
Ahead of this week's Prime Day, which ended early Wednesday, neither Wal-Mart nor Jet.com had announced any official plans to compete with Amazon directly this year.
In 2016, Wal-Mart offered a free 30-day trial for ShippingPass, its competitor at the time to Amazon Prime, around the event. Wal-Mart has since shuttered the program, replacing it with a promise that shoppers will receive free two-day shipping as long as they spend at least $35 online.
In an email, a Wal-Mart spokeswoman told CNBC the company offers "great deals every day."
"[In 2017], we launched free, two-day shipping with no membership fee. ... And, customers can often get even lower prices at Walmart through the Pickup Discount," the spokeswoman said.
A representative from Jet.com, which Wal-Mart acquired in late 2016 in order to boost the big-box retailer's online presence, did not immediately respond to CNBC's request for comment. But from the looks of Jet.com's homepage, the e-retailer didn't offer any exclusive deals around Prime Day.
Marc Lore, Jet.com's co-founder, is no stranger to e-commerce and Amazon. He was the co-founder of Quidsi, the company behind Diapers.com and Soap.com, which Amazon bought for $550 million in 2010. Recently, however, Amazon decided to shut down its Quidsi unit as it failed to make money.
When it first opened for business, Jet.com was already promising cheaper prices than Amazon, aiming to deliver bigger savings to its customers who buy multiple items in a single order.
On Prime Day this year, Wal-Mart had the greatest overlap in its online product assortment compared to Amazon's, Market Track found.
Among the retailers that the firm tracked, 82 percent of the 52 Amazon products observed were also stocked at Walmart.com on Prime Day. Jet.com and Target had 50 percent of those items stocked, and Best Buy had 38 percent, Market Track added.
The table above shows a detailed price comparison for select items at the various retailers on Prime Day, according to Market Track's research.
"There's only one person really geared to fight back, and it's called Wal-Mart," retail consultant Jan Kniffen of J. Rogers Kniffen told CNBC's "Worldwide Exchange" on Wednesday morning.
"I think [Wal-Mart] is doing a great job," Kniffen said. "I think they're the biggest threat to Amazon. I think the two of them battle it out in grocery, they battle it out in the rest of retailing, they battle it out online, and they're going to battle it out in brick-and-mortar now."
Kniffen said he expects Prime Day to be a bigger and bigger event in the coming years — not running out of momentum anytime soon. "I kind of think for retailing [this] is hilarious and scary, both. Nobody does any business in July."
"Amazon intends to take over the world, and they're doing a pretty darn good job of it."