The Cupertino, Calif., company touted the 13 million as a record. "Sales for iPhone 6s and iPhone 6s Plus have been phenomenal, blowing past any previous first weekend sales results in Apple's history," CEO Tim Cook said in a statement.
The 13 million included units sold in Apple's own retail outlets, those through carrier and retail partners' stores, as well as those delivered from pre-sales on its online store. Pre-sales began Sept 12.
Apple's claims -- it has regularly trumpeted early iPhone sales -- are important, analysts said.
"A good start does matter," said Patrick Moorhead, principal analyst with Moor Insights & Strategy. "It shows how competitive demand was [to last year] and shows what pent-up demand there was for the new. Apple is really competing a lot with themselves, so numbers like this mean more to them than to other manufacturers."
Ezra Gottheil of Technology Business Research agreed. "It shows that the iPhone continues to be the sales engine at Apple," Gottheil said.
This year, Apple extended the length of time for pre-sales.
In 2014, Apple opened pre-orders Sept. 12, followed a week later with in-store sales, and wrapped up the sales span at day's end of Sept. 21. The 10 million in sales last year was during a 10-day stretch, inclusive of both the start and end dates.
Meanwhile, this year Apple began taking pre-orders on Sept. 12, started selling the new iPhones Sept. 25, and ended the sale period Sept. 27. The sales span was thus 16 days -- again inclusive of start and end dates -- or 60% longer than in 2014.
Both Moorhead and Gottheil discounted the six additional days of pre-sales as accounting for the jump from 10 million to 13 million.
"There's a certain amount of sales during the pre-sale period, so having more days wouldn't really have an impact," Gottheil said. He added that customers who pre-ordered were those who "absolutely wanted to make sure they got the new iPhone," with the result that the bulk of pre-orders are front-loaded onto the sales period.
"[Having China at the debut] was incredibly important, much more important than the number of pre-sale days," Gottheil continued.
In 2014, the iPhone 6 and 6 Plus were not available in the People's Republic of China (PRC) during Apple's first release wave; Apple kicked off sales there on Oct. 17, four weeks after debuting the new models in the U.S. and nine other markets.
This year, Apple included China in its first wave, along with the U.S. and 11 other markets. (Besides the PRC, the other new-in-2015 market was New Zealand.)
In fact, most analysts -- who had predicted sales in the 12 million to 13 million range for the iPhone 6S/6S Plus opening -- had based their higher-than-2014 forecasts largely on the basis of the earlier launch in China.
Currently, the iPhone 6S and 6S Plus are backordered in the six markets -- the U.S., Australia, Canada, China, Japan and the U.K. -- monitored by the iPhone 6S Pre-Order Tracker, which scrapes Apple's online stores to determine the models, storage configurations and carrier options that are backordered, and by how long.
As of Monday, the tracker listed delays between new orders and shipping that ranged from one to four weeks, depending on the model, color and storage allotment.