Tuesday morning  ChannelAdvisor, which tracks monthly same-store sales growth for third-party sellers on the Amazon and eBay marketplaces, announced sales trends for the month of March.

According to ChannelAdvisor, growth of Amazon’s third-party sales accelerated to 26.2% in March from 23.0% in February, and 14% in January (see exhibit 1). On a two-year stacked basis, third-party sales were consistent with February’s results of 58% growth, which improved from the 48% growth rate in January.

Amazon’s third-party sales have solidly outpaced eBay during the first quarter, and growth was eight percentage points greater in March. When looked at on a two-year basis, Amazon’s outperformance was 21 percentage points better than eBay in March.

Amazon, which reports its first-quarter results later this month, provided guidance for total revenue growth in the range of 13% to 24% for the first quarter. The average of the three months of third-party sales growth is roughly 21%, slightly higher than the midpoint of the guidance range. Historically, Amazon has beaten the midpoint of its revenue guidance range by 3%, which would match the current consensus sales estimates for the first quarter.