Retail giants Walmart and Amazon have been competitors for many years now, with Walmart arguably on its heels for most of it. But the tide might be turning, according to a recent survey conducted by First Insight, a retail analytics firm.

As CNBC reported, First Insight surveyed 3,000 consumers starting in December 2017 through this September. They found that the frequency of people buying items on Amazon six times or more per month has dropped to 40 percent, down from 80 percent in 2017, with Walmart the benefactor. In fact, 55 percent said they prefer to shop at Walmart versus Amazon, up from 47 percent just a year ago. Those preferring to shop at Amazon dropped to 45 percent, down from 53 percent.

When 265 million people shop at Walmart each week and Amazon has 100 million Prime members, each percentage point can feel like a tidal wave of a shift.

Why the shift is happening.

First Insight CEO Craig Petro told CNBC he believes the shift is happening because the novelty and excitement of receiving that Amazon box on your front porch is wearing off. He also believes that something else is working to Walmart's favor that you just wouldn't expect --speed. Says Petro, ?Walmart's speed is allowing them to leapfrog and get hyper-competitive with Amazon in a short period of time."

This is particularly true in the raging battleground that is home grocery delivery. Walmart recently announced it's expanding home grocery delivery to 1,400 stores after a brief test earlier in the year--it will undoubtedly be able to leverage its many more stores in the future. This is meant to compete against Amazon's recent announcement that it was making two-hour grocery delivery available for Prime members.

The point that Walmart is moving fast shouldn't go unappreciated. Working at Procter & Gamble for 24 years, I called on the Bentonville behemoth many times and was always astonished at how slow they were in implementing change. E-commerce changed all that. I watched them buy online retailer and use it as a base to build upon for e-sales.

They moved with a speed I hadn't seen before, launching test after test in e-commerce, overhauling their online selling platform, and demanding change after change from their manufacturing partners to keep pace and to help accelerate the e-push. E-commerce sales were up 37 percent in the latest quarterly earnings report.

What it means for the holidays.

It's all setting up for an epic battle this holiday season, which has six fewer days than usual. I learned through experience that momentum is everything in retail. Walmart is gaining more shoppers; Amazon is losing more. Both will fight tooth and nail to continue and reverse those trends, respectively.

From a strategy perspective, both have committed to winning on similar fronts like online (of course) and home delivery. Both need to win big during the holidays (which account for 20 percent of annual sales on average, according to the National Retail Federation), so they will both be pulling heavily on promotion again this holiday. In fact, Walmart started holiday shopping efforts six days before Halloween this year, it's earliest gambit ever.

Much of the results will come down to execution. I saw it every year across retailers I worked with at P&G. The retailers who had the best holiday seasons executed well. They had the right things in stock, well-displayed at competitive prices, and kept organized stores (even with the crush of shoppers). They had enough staff in the store, merchandised the right things, and created delight for shoppers.

Winning the holidays often means winning the year and capturing momentum into the next year. And with Amazon and Walmart in such a heated battle for that precious momentum, it's going to be a heck of a holiday season.