The latest figures from e-commerce services firm ChannelAdvisor (ECOM) - Get Reportsuggest Alphabet's(GOOGL) - Get Report Google is still seeing strong momentum for its shopping ads, and that eBay (EBAY) - Get Reportcontinues to narrow its market share losses.

For Amazon (AMZN) - Get Report, the numbers don't look great at first glance, but get better with some context.

ChannelAdvisor, which provides a number of services to small and mid-sized online merchants, reports its clients saw a 43.1% annual increase in sales derived from Google Shopping ads. That's better than the 34.3% growth reported for July, and the highest growth rate since last September.

Google Shopping ads, which appear in both Google search results and on the standalone Google Shopping site, were a key reason (along with YouTube ads and general mobile search ad growth) that paid clicks on Google's sites rose 37% in the second quarter over the previous year.

The search giant has been prominently featuring Shopping ads within mobile search results, and has also sought to boost conversion (purchase) rates by allowing users to pay for listed items on Google's site, using payment data previously shared with Google. Google Shopping has been a key part of the search giant's efforts to keep its ad sales from being hurt by consumers going directly to third-party sites and apps -- especially Amazon's.

One slight negative for Google: Client sales from other search ads, whether on Google, Yahoo or Bing, fell 2.6%. But these sales have been pressured for a while thanks to Google Shopping ad adoption, and August's decline is better than the double-digit drops seen earlier this year.

Alphabet is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells GOOGL? Learn more now.

Meanwhile, ChannelAdvisor clients saw their eBay same-store sales (SSS) rise 5.9% annually in August. That's still below the roughly 15% growth research firm comScore estimates for the total U.S. e-commerce market, but up from July's 3.5% growth and the highest growth rate recorded by eBay since February. It's also better than the 3% gross merchandise volume (GMV) growth eBay reported for the second quarter.

Growth was driven by a 13.9% SSS increase for the eBay Motors car-buying site, and a 3.1% increase in fixed-price marketplace sales. Auction sales, which eBay has been de-emphasizing relative to fixed-price sales, fell 15.9%.

The improvements eBay has been making to its oft-criticized shopping experience appear to be paying off. These include using machine learning to deliver better product recommendations, as well as the company's structured data initiative, through which eBay is tagging and organizing listings so as to make them better resemble listings on other e-commerce sites.

As for Amazon, clients selling there witnessed a 10.5% SSS increase. That's better than July's 6.4%, but is still the second-lowest figure reported for the last 12 months. It's also well below the 28% second-quarter sales growth reported for Amazon's North American segment, and the 30% growth reported for its International segment.

But there's a catch: ChannelAdvisor reports seeing "a dramatic increase" in the amount of competition on Amazon's third-party seller marketplace over the last 6 months, which has led its older Amazon clients to lose share to new entrants. As evidence, the company notes that a July seller sample found a 227% annual increase in competing offers for individual products on Amazon.

Also, ChannelAdvisor's data suggests Amazon's fulfillment services for third-party sellers (FBA) continue seeing strong uptake, as sellers use them both for convenience and to make goods eligible for Amazon Prime. 41.1% of all client Amazon sales relied on FBA, up from 33.8%. 2.5% of non-Amazon sales also relied on FBA, but that was down from 3%.

Perhaps the one broader takeaway from ChannelAdvisor's numbers is that U.S. e-commerce growth still looks pretty healthy. While the market's sheer size is bound to be a headwind in the coming years, there's still a lot of share to take from bricks-and-mortar retailers, and the market's biggest names continue improving their offerings to take advantage of that opportunity.