Walmart reported fiscal first-quarter earnings today that showed a huge spike in e-commerce sales as it slightly beat analyst expectations on the bottom line and slightly missed on revenue. Should Amazon be worried? Maybe. Should brand marketers be worried? Definitely.

Here are four key takeaways.

Walmart's momentum continued. The giant was well within its own target as U.S. comp-store-sales grew 1.4%, continuing a three-year run. This came during a quarter where many rivals disappointed, and Target's "good news" was that its comps fell only 1.3%.

E-Commerce delivered big: E-commerce actually accounted for more than half (0.8 points) of Walmart U.S. comp-store growth as sales soared 63%, more than half from organic growth of Walmart.com rather than acquisition of Jet.com or smaller deals.

Adopting free two-day shipping on minimum orders of $35 without an Amazon Prime-like annual fee appears to be a winner. And a newer program giving people discounts to pick up online orders at stores is also helping get people into stores more often. Walmart also cited a huge increase in online assortment, fueled largely by more third-party vendors, up to 50 million items from 10 million a year ago. Bernstein analyst Brandon Fletcher in a note also cites improved website operations and search functionality.

Should Amazon be worried? At least at this pace, Walmart could get to a fifth Amazon's size this year in U.S. e-commerce, up from a sixth last year. Of course, Amazon is currently profitable (if thinly). Walmart e-commerce isn't.

Walmart was more cause than victim of first-quarter retail woes: Rising gas prices, late tax refunds, the peregrinations of the Easter Bunny -- none of that hurt Walmart like it did others. Its comp sales did grow slower than traffic as fewer big-ticket items sold. Walmart blamed later tax refunds. But its more aggressive pricing and e-commerce push clearly took a toll on rivals.

Brand marketers (and rivals) should worry: One illustration of price cutting -- that 63% increase in online sales came on a 69% increase in merchandise volume. Fletcher said Walmart executives acknowledged in a private call with analysts that private label is up as a share of sales. Comp-store inventory also fell 7.3% despite the 1.4% sales increase, an 8.7-point spread nearly as big as the prior quarter's 9. So everyone's biggest retail customer keeps selling more stuff than it buys. All that, and competitive reactions it inevitably provokes, means more pressure to cut prices and costs.