Amazon.com, Inc. AMZN saw its largest two-day period for third-party sales when it hosted its Prime Day event on Tuesday and Wednesday.

What Happened: Third-party gross merchandising value during Amazon's Prime Day event rose an estimated 60% from last year to $3.6 billion and represented 40% of the estimated $8.95 billion (up 60% year-over-year) in total GMV, BofA's Justin Post wrote in a note.

Amazon said last year that its platform facilitated the sale of 175 million items but the company didn't offer a similar metric this year.

Amazon also expanded its Prime Day event from 18 countries last year to 20 this year.

Why It's Important: Coinciding with Amazon's event, other retailers hosted their own sales that should be seen as a positive event for the broader e-commerce industry. Most notably, data from Salesforce found that non-Amazon e-commerce sales on Tuesday rose 69% globally and 76% in the U.S. versus last year.

Post said Amazon also underperformed expectations from eMarketer that modeled $10 billion in GMV during Prime Day so estimates just shy of $9 billion might be "somewhat underwhelming."

What's Next: Amazon's GMV growth rate during Prime Day is still positive compared to BofA Securities 31% GMV growth estimate for the fourth quarter.

The analyst maintains a Buy rating on Amazon's stock with a $3,560 price target.