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So much for concerns that the second Prime Day event wouldn't live up to Amazon's expectations.

The online retailer said Wednesday that the self-created sales holiday was its biggest day ever, with worldwide orders rising more than 60 percent compared with the previous Prime Day. In the U.S., orders rose by more than 50 percent.

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Amazon shares rose slightly, near $752, in early trading Wednesday.

Read More from CNBC: Some of the Best, and Strangest, Deals on Amazon's Prime Day Sale

The retailer's shares ended the prior day slightly lower following concerns over a midday sales update from ChannelAdvisor. The e-commerce software company, which helps power the online operations of roughly 3,000 retailers, said Prime Day sales for its customers selling on Amazon were flat with the prior year's event.

But Piper Jaffray analyst Gene Munster cautioned investors about overreacting to that data point, as ChannelAdvisor's numbers represent just a sample of Amazon's sellers, he said. He added that the figures only capture same-store sales trends; and given that the number of vendors participating in Prime Day was more than double the prior year, they did not capture the complete picture.

Read More from CNBC: Amazon Fixes Prime Day Checkout Issue

Meanwhile, Amazon spread out its deals further into the day, including more than 8,000 of its limited-time "Lightning Deals" launching well into the evening. The retailer said Prime members saved more than double the amount they did last Prime Day — and is already working to amp them up for next year's event.

"After yesterday's results, we'll definitely be doing this again," Greg Greeley, vice president of Amazon Prime, said in a press release announcing the results.